Image sensing device and photographing device including the same

ABSTRACT

An image sensing device and a photographing device including the same are disclosed. The image sensing device includes a pixel array configured to have a first pixel and a second pixel that are different from each other in terms of at least one of an effective measurement distance, temporal resolution, spatial resolution, and unit power consumption, and a timing controller configured to determine whether a distance to a target object is equal to or less than a predetermined threshold distance, and selectively activate any one of the first pixel and the second pixel according to the result of determination.

CROSS-REFERENCE TO RELATED APPLICATION

This patent document claims the priority and benefits of Korean patentapplication No. 10-2020-0067574, filed on Jun. 4, 2020, the disclosureof which is incorporated by reference in its entirety as part of thedisclosure of this patent document.

TECHNICAL FIELD

The technology and implementations disclosed in this patent documentgenerally relate to an image sensing device for sensing a distance to atarget object using a Time of Flight (TOF) method, and a photographingdevice including the same.

BACKGROUND

An image sensor is a semiconductor device for capturing optical imagesby converting light that is incident thereon into electrical signalsusing a semiconductor material that reacts to light. With the recentdevelopment of computer industries and communication industries, demandfor high-performance image sensors has been rapidly increasing invarious electronic devices, for example, smartphones, digital cameras,video game consoles, devices for use with the Internet of Things (IoT),robots, surveillance cameras, medical micro-cameras, etc.

Image sensors may be broadly classified into CCD (Charge Coupled Device)image sensors and CMOS (Complementary Metal Oxide Semiconductor) imagesensors. CCD image sensors may have less noise and better image qualitythan CMOS image sensors. However, CMOS image sensors have a simpler andmore convenient driving scheme, and thus may be preferred in someapplications. In addition, CMOS image sensors may allow a signalprocessing circuit to be integrated into a single chip, which makes iteasy to miniaturize CMOS image sensors for implementation in a product,with the added benefit of consuming very low power. CMOS image sensorscan be fabricated using a CMOS fabrication technology, which results inlow manufacturing costs. CMOS image sensors have been widely used due totheir suitability for implementation in a mobile device.

SUMMARY

Various embodiments of the disclosed technology relate to an imagesensing device for sensing a distance to a target object by changing anoperation mode, and a photographing device including the same.

In one aspect, an image sensing device is provided to include a pixelarray configured to include at least one first pixel and at least onesecond pixel; and a timing controller configured to activate either thefirst pixel or the second pixel based on a distance between a targetobject and the pixel array, wherein the first pixel and the second pixelhave different characteristics that include at least one of an effectivemeasurement distance related to an ability to effectively sense adistance, a temporal resolution related to an ability to discern atemporal difference, a spatial resolution related to an ability todiscern a spatial difference, or unit power consumption indicating anamount of power required to generate a pixel signal.

In another aspect, an image sensing device is provided to include apixel array configured to include at least one first pixel configured tomeasure a distance to a target object using time for light emitted fromthe target object to arrive at the pixel array and at least one secondpixel configured to measure the distance to the target object using aphase of light reflected from the target object; and a timing controllerconfigured to activate either the first pixel or the second pixel basedon a distance between the target object and the pixel array.

In another aspect, a photographing device is provided to include animage sensing device configured to include a first pixel and a secondpixel that are different from each other in terms of at least one of aneffective measurement distance, temporal resolution, spatial resolution,and unit power consumption, and an image signal processor configured todetermine whether a distance to a target object is equal to or less thana predetermined threshold distance, and determine an operation mode ofthe image sensing device to be an object monitoring mode in which thefirst pixel is activated or a depth resolving mode in which the secondpixel is activated.

In another aspect, a photographing device is provided to an imagesensing device configured to have a first pixel and a second pixeldifferent from the first pixel in having different values of at leastone of an effective measurement distance, temporal resolution related toan ability to discern a temporal difference, spatial resolution relatedto an ability to discern a spatial difference, or unit power consumptionindicating an amount of power required to generate a pixel signal; andan image signal processor configured to operate the image sensing devicein an object monitoring mode in which the first pixel is activated or adepth resolving mode in which the second pixel is activated based on acomparison between a predetermined threshold distance and a distancebetween the pixel array and the target object.

In another aspect, a sensing device capable of detecting a distance toan object is provided to comprise: one or more first sensing pixelsconfigured to detect light and measure a distance to a target objectbased on a first distance measuring technique; a first pixel drivercoupled to and operable to control the one or more first sensing pixelsin detecting light for measuring the distance; one or more secondsensing pixels configured to detect light and measure a distance to atarget object based on a second distance measuring technique that isdifferent from the first distance measuring technique so that the firstand second distance measuring techniques have different distancemeasuring characteristics; a second pixel driver coupled to and operableto control the one or more second sensing pixels in detecting light formeasuring the distance; and a controller configured to activate eitherthe one or more first sensing pixels or the one or more second sensingpixels based on the different distance measuring characteristics of thefirst and second sensing pixels with respect to a distance between thetarget object and the sensing device.

It is to be understood that both the foregoing general description andthe following detailed description of the disclosed technology areillustrative and explanatory and are intended to provide furtherexplanation of the disclosure as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and beneficial aspects of the disclosedtechnology will become readily apparent with reference to the followingdetailed description when considered in conjunction with theaccompanying drawings.

FIG. 1 is a block diagram illustrating an example of a photographingdevice based on some implementations of the disclosed technology.

FIG. 2 is a conceptual diagram illustrating an example of operations foreach mode of the image sensing device shown in FIG. 1 based on someimplementations of the disclosed technology.

FIG. 3 is a flowchart illustrating an example of operations for eachmode of the image sensing device shown in FIG. 1 based on someimplementations of the disclosed technology.

FIG. 4 is an equivalent circuit illustrating an example of a directpixel included in a direct pixel array shown in FIG. 1 based on someimplementations of the disclosed technology.

FIG. 5 is an equivalent circuit illustrating an example of an indirectpixel included in an indirect pixel array shown in FIG. 1 based on someimplementations of the disclosed technology.

FIG. 6 is a plan view illustrating an example of the indirect pixelshown in FIG. 5 based on some implementations of the disclosedtechnology.

FIG. 7 is a conceptual diagram illustrating how photocharges are movingby circulation gates in the indirect pixel shown in FIG. 6 based on someimplementations of the disclosed technology.

FIG. 8 is a conceptual diagram illustrating how photocharges are movingtoward a floating diffusion (FD) region by transfer gates in theindirect pixel shown in FIG. 6 based on some implementations of thedisclosed technology.

FIG. 9 is a timing diagram illustrating an example of operations of theimage sensing device based on some implementations of the disclosedtechnology.

FIG. 10 is a schematic diagram illustrating an example of someconstituent elements included in the image sensing device shown in FIG.1 based on some implementations of the disclosed technology.

FIG. 11 is a conceptual diagram illustrating an example of operations ofthe image sensing device shown in FIG. 10 based on some implementationsof the disclosed technology.

FIG. 12 is a conceptual diagram illustrating another example ofoperations of the image sensing device shown in FIG. 1 based on someimplementations of the disclosed technology.

FIG. 13 is a conceptual diagram illustrating an example of operations ofthe image sensing device shown in FIG. 12 based on some implementationsof the disclosed technology.

DETAILED DESCRIPTION

This patent document provides implementations and examples of an imagesensing device and a photographing device including the image sensingdevice. Some implementations of the disclosed technology relate tosensing a distance to a target object by changing an operation mode. Thedisclosed technology provides various implementations of an imagesensing device which can select an optimum Time of Flight (TOF) methodbased on a distance to a target object, and can thus sense the distanceto the target object using the optimum TOF method.

Reference will now be made in detail to the embodiments of the disclosedtechnology, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a block diagram illustrating an example of a photographingdevice based on some implementations of the disclosed technology.

Referring to FIG. 1, the photographing device may refer to a device, forexample, a digital still camera for capturing still images or a digitalvideo camera for capturing moving images. For example, the photographingdevice may be implemented as a Digital Single Lens Reflex (DSLR) camera,a mirrorless camera, or a mobile phone (especially, a smartphone), andothers. The photographing device may include a device having both a lensand an image pickup element such that the device can capture (orphotograph) a target object and can thus create an image of the targetobject.

The photographing device may include an image sensing device 100 and animage signal processor 200.

The image sensing device 100 may measure the distance to a target objectusing a Time of Flight (TOF) method to measure the time for the light totravel between the image sensing device 100 and the target object. Theimage sensing device 100 may include a light source 10, a lens module20, a pixel array 110, a first pixel driver labeled as “direct pixeldriver 120,” a second pixel driver labeled as “indirect pixel driver130,” a direct readout circuit 140, an indirect readout circuit 150, atiming controller 160, and a light source driver 170.

The light source 10 may emit light to a target object 1 upon receiving aclock signal carried by a modulated light signal (MLS) from the lightsource driver 170. The light source 10 may be a laser diode (LD) or alight emitting diode (LED) for emitting light (e.g., near infrared (NIR)light, infrared (IR) light or visible light) having a specificwavelength band, or may be any one of a Near Infrared Laser (NIR), apoint light source, a monochromatic light source combined with a whitelamp or a monochromator, and a combination of other laser sources. Forexample, the light source 10 may emit infrared light having a wavelengthof 800 nm to 1000 nm. Although FIG. 1 shows only one light source 10 forconvenience of description, other implementations are also possible, anda plurality of light sources may also be arranged in the vicinity of thelens module 20.

The lens module 20 may collect light reflected from the target object 1,and may allow the collected light to be focused onto pixels of the pixelarray 110. For example, the lens module 20 may include a focusing lenshaving a surface formed of glass or plastic or another cylindricaloptical element having a surface formed of glass or plastic. The lensmodule 20 may include a single lens group of one or more lenses.

The pixel array 110 may include a plurality of pixels (PXs)consecutively arranged in a two-dimensional (2D) matrix structure forcapturing and detecting incident light for measuring distances. Thepixels are arranged in a column direction and a row directionperpendicular to the column direction. Each pixel (PX) may convertincident light received through the lens module 20 into an electricalsignal corresponding to the amount of incident light, and may thusoutput a pixel signal using the electrical signal. In implementations,the device can be configured so that the pixel signal may not indicatethe color of the target object 1, and may be a signal indicating thedistance to the target object 1.

The pixel array 110 may include, in addition to the imaging pixels, afirst pixel array 112, “direct pixel array,” which includes sensingpixels called “direct pixels” which are capable of sensing the distanceto the target object 1 using a first technique for measuring the TOFsuch as a direct TOF method as further explained below, and a secondpixel array 114, “indirect pixel array,” which includes sensing pixelscalled “indirect pixels” which are capable of sensing the distance tothe target object 1 using a second technique for measuring the TOFdifferent from the first technique, such as an indirect TOF method asfurther explained below. The two pixel arrays 112 and 114 performing theTOF measurement for determining the distance may have different TOFcharacteristics, e.g., the first TOF technique may have a longereffective measurement distance and a lower spatial resolution, and thesecond TOF technique may have a higher spatial resolution and a shortereffective measurement distance. The inclusion of two or more suchdifferent TOF sensing pixels enable the device to detect objects locatedboth near and far from the image sensing device while allowing suchdifferent TOF sensing pixels to complement one another and tocollectively provide the ability of sensing objects at varyingdistances. In operation, a control circuit is provided to select one ofthe two pixel arrays 112 and 114 to measure a distance to a targetobject based on the different distance measuring characteristics of thetwo pixel arrays 112 and 114 to optimize the performance of distancemeasurements.

Referring to FIGS. 1 and 10, the direct pixels 1010 may be arranged in aline sensor shape within the pixel array 1005, such that the entireregion including the direct pixels 1010 arranged in the line sensorshape may be smaller in size than the region including the indirectpixels 1040. This is because the direct pixels 1010 are designed to havea relatively longer effective measurement distance and a relativelyhigher temporal resolution rather than a purpose of acquiring anaccurate depth image. As a result, the direct pixels 1010 can recognizethe presence or absence of the target object 1 in the object monitoringmode using the relatively longer effective measurement distance and therelatively higher temporal resolution, and at the same time cancorrectly measure the distance to the target object 1 using therelatively longer effective measurement distance and the relativelyhigher temporal resolution.

As an example of the first technique for measuring TOF, the direct TOFmethod may directly measure a round trip time from a first time wherepulse light is emitted to the target object 1 to a second time wherepulse light reflected from the target object 1 is incident, and may thuscalculate the distance to the target object 1 by using the round triptime and the speed of light. As an example of the second technique formeasuring TOF, the indirect TOF method may emit light modulated by apredetermined frequency to the target object 1, may sense modulatedlight that is reflected from the target object 1, may calculate a phasedifference between a clock signal MLS controlling the modulated lightand a pixel signal generated from detecting the modulated lightreflected back from the target object 1, and may thus calculate thedistance to the target object 1 based on the phase difference betweenthe clock signal MLS and the pixel signal. Generally, whereas the directTOF method may have advantages in that it has a relatively highertemporal resolution and a longer effective measurement distance, thedirect TOF method may have disadvantages in that it has a relativelylower spatial resolution due to a one-to-one correspondence structurebetween each pixel and each readout circuit.

The spatial resolution may be used to refer to the ability to discern aspatial difference. As each pixel is reduced in size, the spatialresolution may increase. Temporal resolution may be used to refer to theability to discern a temporal difference. As time required by the pixelarray 110 for outputting a pixel signal corresponding to a single frameis shortened, the temporal resolution may increase.

A time needed by each sensing pixel for measuring the TOF using thefirst or the second TOF measurement technique is referred to a unitsensing time. The power used during the unit sensing time by eachsensing pixel for measuring the TOF is referred to as a unit powerconsumption. In some implementations in which the sensing pixel formeasuring the TOF using the first technique is configured to receive arelatively high reverse bias voltage as will be described later, suchsensing pixel may have a relatively higher unit power consumption thanthat of the sensing pixel measuring the TOF using the second technique.

In some implementations, the direct pixel may be a single-photonavalanche diode (SPAD) pixel. The operation principles of the SPAD pixelare as follows. A reverse bias voltage may be applied to the SPAD pixelto increase an electric field, resulting in formation of a strongelectric field. Subsequently, there may occur impact ionization in whichelectrons generated by photons that are incident by the strong electricfield move from one place to another place to generate electron-holepairs. Specifically, in the SPAD pixel configured to operate in a Geigermode in which a reverse bias voltage higher than a breakdown voltage isreceived, carriers (electrons or holes) generated by incident light maycollide with electrons and holes generated by the above impactionization, such that a large number of carriers may be generated bysuch collision. Accordingly, although a single photon is incident uponthe SPAD pixel, avalanche breakdown may be triggered by the singlephoton, resulting in formation of a measurable current pulse. A detailedstructure and operations of the SPAD pixel will be described later withreference to FIG. 4.

In some implementations, the indirect pixel may be a circulation pixel.In the circulation pixel, a first operation of moving, in apredetermined direction (e.g., a clockwise or counterclockwisedirection), of photocharges generated by a photoelectric conversionelement in response to reflected light and a second operation oftransferring of photocharges collected by such movement to a pluralityof floating diffusion (FD) regions can be performed separately from eachother. For example, each circulation pixel may include a plurality ofcirculation gates and a plurality of transfer gates that surround thephotoelectric conversion element. Potential of circulation gates andpotential of transfer gates may be changed while being circulated in apredetermined direction. Photocharges generated by the photoelectricconversion element may move and transfer in a predetermined direction bya change in circulation potential between the circulation gates and thetransfer gates. As described above, movement of photocharges andtransfer of photocharges may be performed separately from each other,such that a time delay based on the distance to the target object 1 canbe more effectively detected. A detailed structure and operations of thecirculation pixel will be described later with reference to FIGS. 5 to8. In addition, photocharges mentioned in the disclosed technology maybe photoelectrons.

The direct pixel driver 120 may drive the direct pixel array 112 of thepixel array 110 in response to a control signal from the timingcontroller 160. For example, the direct pixel driver 120 may generate aquenching control signal to control a quenching operation for reducing areverse bias voltage applied to the SPAD pixel to a breakdown voltage orless. In addition, the direct pixel driver 120 may generate a rechargingcontrol signal for implanting charges into a sensing node connected tothe SPAD pixel.

The indirect pixel driver 130 may drive the indirect pixel array 114 ofthe pixel array 110 in response to a control signal from the timingcontroller 160. For example, the indirect pixel driver 130 may generatea circulation control signal, a transfer control signal, a reset controlsignal, and a selection control signal. In more detail, the circulationcontrol signal may control movement of photocharges within aphotoelectric conversion element of each pixel. The transfer controlsignal may allow moved photocharges to be sequentially transferred tothe floating diffusion (FD) regions. The reset control signal mayinitialize each pixel. The selection control signal may control outputof an electrical signal corresponding to a voltage of the floatingdiffusion (FD) regions.

The direct readout circuit 140 may be disposed at one side of the pixelarray 110, may calculate a time delay between a pulse signal generatedfrom each pixel of the direct pixel array 112 and a reference pulse, andmay generate and store digital data corresponding to the time delay. Thedirect readout circuit 140 may include a time-to-digital circuit (TDC)configured to perform the above-mentioned operation. The direct readoutcircuit 140 may transmit the stored digital data to the image signalprocessor 200 under control of the timing controller 160.

The indirect readout circuit 150 may process an analog pixel signalgenerated from each pixel of the indirect pixel array 114, and may thusgenerate and store digital data corresponding to the pixel signal. Forexample, the indirect readout circuit 150 may include a correlateddouble sampler (CDS) circuit for performing correlated double samplingon the pixel signal, an analog-to-digital converter (ADC) circuit forconverting an output signal of the CDS circuit into digital data, and anoutput buffer for temporarily storing the digital data. The indirectreadout circuit 150 may transmit the stored digital data to the imagesignal processor 200 under control of the timing controller 160.

The timing controller 160 may control overall operation of the imagesensing device 100. Thus, the timing controller 160 may generate atiming signal to control operations of the direct pixel driver 120, theindirect pixel driver 130, and the light source driver 170. In addition,the timing controller 160 may control activation or deactivation of eachof the direct readout circuit 140 and the indirect readout circuit 150,and may control digital data stored in the direct readout circuit 140and digital data stored in the indirect readout circuit 150 to besimultaneously or sequentially transmitted to the image signal processor200.

Specifically, the timing controller 160 may selectively activate ordeactivate the direct pixel array 112, the direct pixel driver 120, andthe direct readout circuit 140 under control of the image signalprocessor 200, or may selectively activate or deactivate the indirectpixel array 114, the indirect pixel driver 130, and the indirect readoutcircuit 150 under control of the image signal processor 200. Operationsfor each mode of the image sensing device 100 will be described laterwith reference to FIGS. 2 and 3.

The light source driver 170 may generate a clock signal carried by amodulated light signal (MLS) capable of driving the light source 10 inresponse to a control signal from the timing controller 160.

The image signal processor 200 may process digital data received fromthe image sensing device 100, and may generate a depth image indicatingthe distance to the target object 1. Specifically, the image signalprocessor 200 may calculate the distance to the target object 1 for eachpixel in response to a time delay denoted by digital data received fromthe direct readout circuit 140. In addition, the image signal processor200 may calculate the distance to the target object 1 for each pixel inresponse to a phase difference denoted by digital data received from theindirect readout circuit 150.

The image signal processor 200 may control operations of the imagesensing device 100. Specifically, the image signal processor 200 mayanalyze (or resolve) digital data received from the image sensing device100, may decide a mode of the image sensing device 100 based on theanalyzed result, and may control the image sensing device 100 to operatein the decided mode.

The image signal processor 200 may perform image signal processing ofthe depth image such that the image signal processor 200 may performnoise cancellation and image quality improvement of the depth image. Thedepth image generated from the image signal processor 200 may be storedin an internal memory of a photographing device, or a device includingthe photographing device or in an external memory either in response toa user request or in an automatic manner, such that the stored depthimage can be displayed through a display. Alternatively, the depth imagegenerated from the image signal processor 200 may be used to controloperations of the photographing device or the device including thephotographing device.

FIG. 2 is a diagram illustrating an example of operations for each modeof the image sensing device 100 shown in FIG. 1 based on someimplementations of the disclosed technology.

Referring to FIG. 2, the photographing device may be embedded in variouskinds of devices, for example, a mobile device such as a smartphone, atransportation device such as a vehicle, a surveillance device such as aclosed circuit television (CCTV), and the others. For convenience ofdescription and better understanding of the disclosed technology, it isassumed that the photographing device shown in FIG. 1 is embedded in avehicle 300. The vehicle 300 including the photographing device willhereinafter be referred to as a host vehicle for convenience ofdescription.

The image sensing device 100 embedded in the host vehicle 300 may sensethe distance to the target object 1 using the direct pixel array 112according to the direct TOF method, or may sense the distance to thetarget object 1 using the indirect pixel array 114 according to theindirect TOF method. As previously stated above, the direct TOF methodmay have a longer effective measurement distance and a lower spatialresolution, and the indirect TOF method may have a higher spatialresolution and a shorter effective measurement distance. Therefore, afirst range within which the direct pixel array 112 can effectivelymeasure the distance to the target object 1 (for example, at a validreliability level corresponding to a predetermined reliability orgreater) will hereinafter be denoted by a first effective measurementregion (EMA1), and a second range within which the indirect pixel array114 can effectively measure the distance to the target object 1 (forexample, at a valid reliability level corresponding to a predeterminedreliability or greater) will hereinafter be denoted by a secondeffective measurement region (EMA2).

In this case, the effective measurement distance may refer to a maximumlength in which the direct pixel array 112 or the indirect pixel array114 can effectively sense the distance to the target object 1 at acertain reliability level that is equal to or greater than apredetermined reliability threshold. Here, the effective measurementdistance of the direct pixel may be longer than that of the indirectpixel.

As can be seen from FIG. 2, a Field of View (FOV) of the first effectivemeasurement region EMA1 may be less than that of the second effectivemeasurement region EMA2.

Operations of the image sensing device 100 based on the direct TOFmethod are as follows. In accordance with the direct TOF method, eachpixel generates a pulse signal when incident light is sensed and as soonas the pulse signal is generated, the readout circuit generates digitaldata indicative of time of flight (TOF) by converting generation time ofthe pulse signal into digital data indicating a time of flight (TOF),and then stores the digital data. Each pixel is configured to generate apulse signal by sensing incident light without the capability to storeinformation, and thus the readout circuit is needed to store informationneeded for distance calculation. As a result, a readout circuit isneeded for each pixel. For example, the readout circuit may be includedin each pixel. However, if the array is configured with the plurality ofpixels, each including the readout circuit, each pixel may haveunavoidable increase in size due to the readout circuit. In addition,since an overall size for a region allocated to the array is restricted,it may be difficult to increase the number of pixels to be included inthe array. Therefore, in some implementations of the disclosedtechnology, the readout circuit may be located outside the pixel arraysuch that as many circuits as possible can be included in the pixelarray. In some implementations, the array including direct pixels may beformed in an X-shape or a cross-shape such that the readout circuit andthe direct pixel may be arranged to correspond to each other on a one toone basis. The above-mentioned operation method may be referred to as aline scanning method. When the readout circuit is located outside thepixel array, even if direct pixels are included in the same row or samecolumn of the pixel array, the direct pixels are not simultaneouslyactivated and only one of the direct pixels on the same row or the samecolumn can be activated.

Operations of the image sensing device 100 based on the indirect TOFmethod are as follows. In accordance with the indirect TOF method, eachpixel may accumulate photocharges corresponding to the intensity ofincident light, and the readout circuit may convert a pixel signalcorresponding to the photocharges accumulated in each pixel into digitaldata and then store the digital data. Each pixel can store informationneeded for distance calculation using photocharges without the readoutcircuit. As a result, pixels can share the readout circuit, and indirectpixels contained in the array including the indirect pixels can besimultaneously driven. The above-mentioned operation method may bereferred to as as an area scanning method.

Therefore, the number of pixels that are simultaneously driven whenusing the line scanning method is relatively smaller than that whenusing the area scanning method. Thus, a field of view (FOV) of the firsteffective measurement region EMA1 of the array including direct pixelsdriven by the line scanning method may be less than an FOV of the secondeffective measurement region EMA2 of the array including indirect pixelsdriven by the area scanning method.

Referring back to FIG. 2, within the range L16 from the host vehicle300, the direct pixel array 112 can effectively measure the distance tothe target object 1. Thus, the range within which the distance to thehost vehicle 300 is denoted by L16 or less will hereinafter be definedas a direct TOF zone. Within the range L4 from the host vehicle 300, theindirect pixel array 114 can effectively measure the distance to thetarget object 1. Thus, the range within which the distance to the hostvehicle 300 is denoted by L4 or less will hereinafter be defined as anindirect TOF zone. Each of L0 to L16 may correspond to a valueindicating a specific distance, and the spacing between Ln (where “n” isany one of 0 to 15) and L(n+1) may be constant. The length of the directTOF zone may be four times the length of the indirect TOF zone. Therange and the length of the direct TOF zone or the indirect TOF zone asdiscussed above are examples only and other implementations are alsopossible.

As can be seen from FIG. 2, it is assumed that first to fourth vehiclesVH1˜VH4 are respectively located at four different positions in aforward direction of the host vehicle 300. Since the first to fourthvehicles VH1˜VH4 are included in the direct TOF zone, the distancebetween the host vehicle 300 and each of the vehicles VH1˜VH4 can besensed using the direct TOF method. However, since the first to thirdvehicles VH1˜VH3 are not included in the indirect TOF zone, the distancebetween the host vehicle 300 and each of the vehicles VH1˜VH3 cannot besensed using the indirect TOF method. Thus, each of the first to thirdvehicles VH1˜VH3 may sense the distance to the host vehicle 300 usingthe direct TOF method only. Meanwhile, since the fourth vehicle VH4 maybe included in the direct TOF zone and in the indirect TOF zone, thefourth vehicle VH4 may sense the distance to the host vehicle 300 usingthe direct TOF method or the indirect TOF method.

A forward region of the host vehicle 300 may be classified into a hotzone and a monitoring zone based on the distance to the host vehicle300. The hot zone may correspond to an area distanced from the hostvehicle 300 by the distance that is equal to or shorter than a thresholddistance (e.g., L4). In the hot zone, the distance to a target object isrelatively short and thus the sensing of the position of the targetobject in the hot zone requires high level of accuracy. The monitoringzone may correspond to an area distanced from the host vehicle 300 bythe distance that is longer than a threshold value (e.g., L4). In themonitoring zone, since the distance to a target object is relativelylong, the sensing of an existence of the target object in a forwardregion (e.g., the presence or an absence of the target object) isrequired while the sensing of the position of the target object in themonitoring does not require that high level of accuracy.

In more detail, in the hot zone, a method for sensing the distance to atarget object using the indirect TOF method having a higher spatialresolution may be considered more advantageous. In the monitoring zone,a method for sensing the distance to a target object using the directTOF method having a longer effective measurement distance may beconsidered more advantageous. For example, the distance to each of thefirst to third vehicles VH1˜VH3 may be more advantageously sensed usingthe direct TOF method, and the distance to the fourth vehicle VH4 may bemore advantageously sensed using the indirect TOF method. As can be seenfrom FIG. 2, the distance to the first vehicle VH1 may be denoted byL13, the distance to the second vehicle VH2 may be denoted by L9, thedistance to the third vehicle VH3 may be denoted by L4, and the distanceto the fourth vehicle VH4 may be denoted by L1.

In some implementations, the hot zone may be identical to the indirectTOF zone, and the monitoring zone may refer to a region obtained bysubtracting the indirect TOF zone from the direct TOF zone. In someother implementations, the hot zone may be larger or smaller than theindirect TOF zone.

Although FIG. 2 shows the exemplary case in which the photographingdevice is embedded in the vehicle as the example, other implementationsare also possible, and the photographing device may be embedded in otherdevices. The method for selectively using the direct TOF method or theindirect TOF method in response to the distance to the target object canbe applied to, for example, a face/iris recognition mode implemented bya wake-up function from among sleep-mode operations of a mobile phone,and can be applied to a surveillance mode for detecting the presence orabsence of a target object using a CCTV, and a photographing mode forprecisely photographing the target object.

FIG. 3 is a flowchart illustrating an example of operations for eachmode of the image sensing device 100 shown in FIG. 1 based on someimplementations of the disclosed technology.

Referring to FIGS. 2 and 3, the image sensing device 100 may operate inan object monitoring mode or in a depth resolving mode under control ofthe image signal processor 200. In the object monitoring mode, thedirect pixel array 112, the direct pixel driver 120, and the directreadout circuit 140 may be activated, the indirect pixel array 114, theindirect pixel driver 130, and the indirect readout circuit 150 may bedeactivated. In the depth resolving mode, the indirect pixel array 114,the indirect pixel driver 130, and the indirect readout circuit 150 maybe activated, the direct pixel array 112, the direct pixel driver 120,and the direct readout circuit 140 may be deactivated.

If the distance sensing operation of the image sensing device 100 isstarted, the image sensing device 100 operates in the object monitoringmode by default and generates digital data indicating the distance to atarget object using the direct TOF method (step S10).

The image sensing device 100 may transmit digital data generated fromthe direct pixel array 112 to the image signal processor 200. The imagesignal processor 200 may calculate a distance to a target object basedon the digital data, and may determine whether the calculated distanceto the target object is equal to or shorter than a threshold distancefor determining the range of a hot zone, such that the image signalprocessor 200 can thus determine whether the target object is detectedin the hot zone (step S20).

If the calculated distance to the target object is longer than thethreshold distance (i.e., “No” in step S20), the image sensing device100 may continuously operate in the object monitoring mode. For example,if the target object is any one of the first to third vehicles VH1˜VH3shown in FIG. 2, the image sensing device 100 may continuously operatein the object monitoring mode.

If the calculated distance to the target object is equal to or shorterthan the threshold distance (i.e., “Yes” in step S20), the image signalprocessor 200 may increase the counted resultant value stored in a modecounter embedded therein by a predetermined value (e.g., “1”). Inaddition, the image signal processor 200 may determine whether thecounted resultant value stored in the mode counter is higher than apredetermined mode switching value K (where K is an integer) in stepS30. If a predetermined time (or an initialization time) has elapsed, orif the operation mode of the image sensing device 100 switches from theobject monitoring mode to the depth resolving mode, the countedresultant value may be initialized. Therefore, within the predeterminedtime (or the initialization time), the image signal processor 200 maydetermine whether a specific event in which the calculated distance tothe target object is equal to or shorter than the threshold distance hasoccurred a predetermined number of times or more. As a result, anexemplary case in which the counted resultant value is unexpectedlychanged due to erroneous detection, or an exemplary case in which thetarget object is temporarily located in the hot zone may be excluded.

If the counted resultant value is equal to or less than a predeterminedmode switching value K (i.e., “No” in step S30), the image sensingdevice 100 may continuously operate in the object monitoring mode. Forexample, if the target object has temporarily existed at the position ofthe fourth vehicle VH4 shown in FIG. 2, or if erroneous detection hasoccurred, the image sensing device 100 may continuously operate in theobject monitoring mode.

If the counted resultant value is higher than the predetermined modeswitching value K (i.e., “Yes” in step S30), the image signal processor200 may allow the operation mode of the image sensing device 100 toswitch from the object monitoring mode to the depth resolving mode.Accordingly, the image sensing device 100 may generate digital dataindicating the distance to the target object using the indirect TOFmethod (step S40). On the other hand, the image signal processor 200 mayperform switching of the operation mode of the image sensing device 100,and may then initialize the counted resultant value.

In addition, if the image signal processor 200 determines that thetarget object 1 is not present in the hot zone based on digital datareceived from the image sensing device 100, the image signal processor200 may finish the depth resolving mode. In this case, the image signalprocessor 200 may control the image sensing device 100 to re-performstep S10.

Therefore, if the distance to the target object is equal to or shorterthan the threshold distance (i.e., if the target object is located inthe hot zone), the image sensing device 100 may sense the distance tothe target object using the indirect TOF method (i.e., by activating theindirect pixel array 114). If the distance to the target object islonger than the threshold value (i.e., if the target object is locatedin the monitoring zone), the image sensing device 100 may sense thedistance to the target object using the direct TOF method (i.e., byactivating the direct pixel array 112). That is, an optimum operationmode can be selected according to the distance to the target object. Inaddition, in the object monitoring mode in which precise distancesensing need not be used, only some direct pixels from among the directpixels may be activated, resulting in reduction in power consumption.Methods for activating the pixels included in the pixel array 110 duringthe respective operation modes will be described later with reference toFIGS. 10 to 13.

FIG. 4 is an equivalent circuit illustrating an example of a directpixel DPX included in the direct pixel array 112 shown in FIG. 1 basedon some implementations of the disclosed technology.

The direct pixel array 112 may include a plurality of direct pixels(DPXs). Although it is assumed that each direct pixel (DPX) shown inFIG. 4 is a single-photon avalanche diode (SPAD) pixel for convenienceof description, other implementations are also possible.

The direct pixel (DPX) may include a single-photon avalanche diode(SPAD), a quenching circuit (QC), a digital buffer (DB), and arecharging circuit (RC).

The SPAD may sense a single photon reflected by the target object 1, andmay thus generate a current pulse corresponding to the sensed singlephoton. The SPAD may be a photodiode provided with a photosensitive P-Njunction. In the SPAD, avalanche breakdown may be triggered by a singlephoton received in a Geiger mode that receives a reverse bias voltagegenerated when a cathode-to-anode voltage is higher than a breakdownvoltage, resulting in formation of a current pulse. As described above,the above-mentioned process for forming the current pulse throughavalanche breakdown triggered by the single photon will hereinafter bereferred to as an avalanche process.

One terminal of the SPAD may receive a first bias voltage (Vov) forapplying a reverse bias voltage (hereinafter referred to as an operationvoltage) higher than a breakdown voltage to the SPAD. For example, thefirst bias voltage (Vov) may be a positive (+) voltage having anabsolute value that is lower than an absolute value of a breakdownvoltage. The other terminal of the SPAD may be coupled to a sensing node(Ns), and the SPAD may output a current pulse generated by sensing thesingle photon to the sensing node (Ns).

The quenching circuit (QC) may control the reverse bias voltage appliedto the SPAD. If a time period (or a predetermined time after pulses ofthe clock signal (MLS) have been generated) in which the avalancheprocess can be carried out has elapsed, a quenching transistor (QX) ofthe quenching circuit (QC) may be turned on in response to a quenchingcontrol signal (QCS) such that the sensing node (Ns) can be electricallycoupled to a ground voltage. As a result, the reverse bias voltageapplied to the SPAD may be reduced to a breakdown voltage or less, andthe avalanche process may be quenched (or stopped).

The digital buffer (DB) may perform sampling of an analog current pulseto be input to the sensing node (Ns), such that the digital buffer (DB)may convert the analog current pulse into a digital pulse signal. Inthis example, the sampling of the analog current pulse may be performedby converting the analog current pulse into the digital pulse signalhaving a logic level “0” or “1” based on a determination whether thelevel of a current pulse is equal to or higher than a threshold level.However, the sampling method is not limited to thereto and otherimplementations are also possible. Therefore, the pulse signal generatedfrom the digital buffer (DB) may be denoted by a direct pixel outputsignal (DPXout), such that the pulse signal denoted by the direct pixeloutput signal (DPXout) can be transferred to the direct readout circuit140.

After the avalanche process is quenched by the quenching circuit (QC),the recharging circuit (RC) may implant or provide charges into thesensing node (Ns) such that the SPAD can re-enter the Geiger mode inwhich avalanche breakdown can be induced. For example, the rechargingcircuit (RC) may include a switch (e.g., a transistor) that canselectively connect a second bias voltage to the sensing node (Ns) inresponse to a recharging control signal. If the switch is turned on, thevoltage of the sensing nose (Ns) may reach the second bias voltage. Forexample, the sum of the absolute value of the second bias voltage andthe absolute value of the first bias voltage may be higher than theabsolute value of the breakdown voltage, and the second bias voltage maybe a negative(−) voltage. Therefore, the SPAD may enter the Geiger mode,such that the SPAD may perform the avalanche process by the singlephoton received in a subsequent time.

In the example, each of the quenching circuit (QC) and the rechargingcircuit (RC) is implemented as an active device, other implementationsare also possible. Thus, in some implementations, each of the quenchingcircuit (QC) and the recharging circuit (RC) may also be implemented asa passive device. For example, the quenching transistor (QX) of thequenching circuit (QC) may also be replaced with a resistor.

The quenching control signal (QCS) and the recharging control signal maybe supplied from the direct pixel driver 120 shown in FIG. 1.

The direct readout circuit 140 may include a digital logic circuitconfigured to generate digital data by calculating a time delay betweena pulse signal of the direct pixel (DPX) and a reference pulse, and anoutput buffer configured to store the generated digital data. Thedigital logic circuit and the output buffer may hereinafter becollectively referred to as a Time-to-Digital Circuit (TDC). In thiscase, the reference pulse may be a pulse of the clock signal (MLS).

FIG. 5 is an equivalent circuit illustrating an example of the indirectpixel IPX included in the indirect pixel array 114 shown in FIG. 1 basedon some implementations of the disclosed technology.

The indirect pixel array 114 may include a plurality of indirect pixels(IPXs). Although it is assumed that each indirect pixel (IPX) shown inFIG. 5 is a circulation pixel for convenience of description, otherimplementations are also possible.

The indirect pixel (IPX) may include a plurality of transfer transistorsTX1˜TX4, a plurality of circulation transistors CX1˜CX4, and a pluralityof pixel signal generation circuits PGC1˜PGC4.

The photoelectric conversion element PD may perform photoelectricconversion of incident light reflected from the target object 1, and maythus generate and accumulate photocharges. For example, thephotoelectric conversion element PD may be implemented as a photodiode,a pinned photodiode, a photogate, a phototransistor or a combinationthereof. One terminal of the photoelectric conversion element PD may becoupled to a substrate voltage (Vsub), and the other terminal of thephotoelectric conversion element PD may be coupled to the plurality oftransfer transistors TX1˜TX4 and the plurality of circulationtransistors CX1˜CX4. In this case, the substrate voltage (Vsub) may be avoltage (for example, a ground voltage) that is applied to the substratein which the photoelectric conversion element PD is formed.

The transfer transistor TX1 may transfer photocharges stored in thephotoelectric conversion element PD to the floating diffusion (FD)region FD1 in response to a transfer control signal TFv1. The transfertransistor TX2 may transfer photocharges stored in the photoelectricconversion element PD to the floating diffusion (FD) region FD2 inresponse to a transfer control signal TFv2. The transfer transistor TX3may transfer photocharges stored in the photoelectric conversion elementPD to the floating diffusion (FD) region FD3 in response to a transfercontrol signal TFv3. The transfer transistor TX4 may transferphotocharges stored in the photoelectric conversion element PD to thefloating diffusion (FD) region FD4 in response to a transfer controlsignal TFv4. Each of the transfer control signals TFv1˜TFv4 may bereceived from the indirect pixel driver 130.

The circulation transistors CX1˜CX4 may be turned on or off in responseto the circulation control signals CXV1˜CXV4. In more detail, thecirculation transistor CX1 may be turned on or off in response to thecirculation control signal CXV1, the circulation transistor CX2 may beturned on or off in response to the circulation control signal CXV2, thecirculation transistor CX3 may be turned on or off in response to thecirculation control signal CXV3, and the circulation transistor CX4 maybe turned on or off in response to the circulation control signal CXV4.One terminal of each of the circulation transistors CX1˜CX4 may becoupled to the photoelectric conversion element PD, and the otherterminal of each of the circulation transistors CX1˜CX4 may be coupledto a drain voltage (Vd). During a modulation period in whichphotocharges generated by the photoelectric conversion element PD arecollected and transmitted to the floating diffusion (FD) regionsFD1˜FD4, the drain voltage (Vd) may be at a low-voltage (e.g., a groundvoltage) level. During a readout period after lapse of the modulationperiod, the drain voltage (Vd) may be at a high-voltage (e.g., apower-supply voltage) level. In addition, the circulation controlsignals CXV1˜CXV4 may respectively correspond to the circulation controlvoltages Vcir1˜Vcir4 (see FIG. 6) during the modulation period, suchthat each of the circulation transistors CX1˜CX4 may enable photochargesgenerated by the photoelectric conversion element PD to move in apredetermined direction (for example, in a counterclockwise direction).In addition, each of the circulation control signals CXV1˜CXV4 maycorrespond to a draining control voltage (Vdrain) (see FIG. 6) duringthe readout period, such that each of the circulation transistorsCX1˜CX4 may fix a voltage level of the photoelectric conversion elementPD to the drain voltage (Vd). Each of the circulation control signalsCXV1˜CXV4 may be received from the indirect pixel driver 130.

The pixel signal generation circuits PGC1˜PGC4 may store photochargestransferred from the transfer transistors TX1˜TX4, and may outputindirect pixel output signals IPXout1˜IPXout4 indicating electricalsignals corresponding to the stored photocharges to the indirect readoutcircuit 150. In more detail, the pixel signal generation circuit PGC1may store photocharges transferred from the transfer transistor TX1, andmay output an indirect pixel output signal IPXout1 indicating anelectrical signal corresponding to the stored photocharges to theindirect readout circuit 150. The pixel signal generation circuit PGC2may store photocharges transferred from the transfer transistor TX2, andmay output an indirect pixel output signal IPXout2 indicating anelectrical signal corresponding to the stored photocharges to theindirect readout circuit 150. The pixel signal generation circuit PGC3may store photocharges transferred from the transfer transistor TX3, andmay output an indirect pixel output signal IPXout3 indicating anelectrical signal corresponding to the stored photocharges to theindirect readout circuit 150. The pixel signal generation circuit PGC4may store photocharges transferred from the transfer transistor TX4, andmay output an indirect pixel output signal IPXout4 indicating anelectrical signal corresponding to the stored photocharges to theindirect readout circuit 150. In some implementations, the pixel signalgeneration circuits PGC1˜PGC4 may be simultaneously or sequentiallyoperated. The indirect pixel output signals IPXout1˜IPXout4 maycorrespond to different phases, and the image signal processor 200 maycalculate the distance to the target object 1 by calculating a phasedifference in response to digital data generated from the indirect pixeloutput signals IPXout1˜IPXout4.

The structures and operations of the pixel signal generation circuitsPGC1˜PGC4 may be discussed later using the pixel signal generationcircuit PGC1 as an example and such descriptions will be also consideredfor the remaining pixel signal generation circuits PGC2˜PGC4. Thus,redundant descriptions for the pixel signal generation circuitsPGC2˜PGC4 will be omitted for brevity.

The pixel signal generation circuit PGC1 may include a reset transistorRX1, a capacitor C1, a drive transistor DX1, and a selection transistorSX1.

The reset transistor RX1 may be coupled between a reset voltage (Vr) andthe floating diffusion (FD) region FD1, and may be turned on or off inresponse to a reset control signal RG1. For example, the reset voltage(Vr) may be a power-supply voltage. Whereas the turned-off resettransistor RX1 can sever electrical connection between the reset voltage(Vr) and the floating diffusion (FD) region FD1, the turn-on resettransistor RX1 can electrically connect the reset voltage (Vr) to thefloating diffusion (FD) region FD1 such that the floating diffusion (FD)region FD1 can be reset to the reset voltage (Vr).

The capacitor C1 may be coupled between the ground voltage and thefloating diffusion (FD) region FD1, such that the capacitor C1 mayprovide electrostatic capacity in a manner that the floating diffusion(FD) region FD1 can accumulate photocharges received through thetransfer transistor TX1. For example, the capacitor C1 may beimplemented as a junction capacitor.

The drive transistor DX1 may be coupled between the power-supply voltage(VDD) and the selection transistor SX1, and may generate an electricalsignal corresponding to a voltage level of the floating diffusion (FD)region FD1 coupled to a gate terminal thereof.

The selection transistor SX1 may be coupled between the drive transistorDX1 and an output signal line, and may be turned on or off in responseto the selection control signal SEL1. When the selection transistor SX1is turned off, the selection transistor SX1 may not output theelectrical signal of the drive transistor DX1 to the output signal line,and when the selection transistor is turned-on, the selection transistorSX1 may output the electrical signal of the drive transistor DX1 to theoutput signal line. In this case, the output signal line may be a linethrough which the indirect pixel output signal (IPXout1) of the indirectpixel (IPX) is applied to the indirect readout circuit 150, and otherpixels belonging to the same column as the indirect pixel (IPX) may alsooutput the indirect pixel output signals through the same output signalline.

Each of the reset control signal RG1 and the selection control signalSEL1 may be provided from the indirect pixel driver 130.

FIG. 6 is a plan view 600 illustrating an example of the indirect pixel(IPX) shown in FIG. 5 based on some implementations of the disclosedtechnology.

Referring to FIG. 6, a plan view 600 illustrating some parts of theindirect pixel (IPX) is illustrated. The plan view 600 illustrating someparts of the indirect pixel (IPX) may include a photoelectric conversionelement PD, a plurality of floating diffusion (FD) regions FD1˜FD4, aplurality of drain nodes D1˜D4, a plurality of transfer gates TG1˜TG4,and a plurality of circulation gates CG1˜CG4. The transfer gates TG1˜TG4may respectively correspond to gates of the transfer transistors TX1˜TX4shown in FIG. 5. Thus, the transfer gate TG1 may correspond to a gate ofthe transfer transistor TX1, the transfer gate TG2 may correspond to agate of the transfer transistor TX2, the transfer gate TG3 maycorrespond to a gate of the transfer transistor TX3, and the transfergate TG4 may correspond to a gate of the transfer transistor TX4. Inaddition, the circulation gates CG1˜CG4 may respectively correspond togates of the circulation transistors CX1˜CX4 shown in FIG. 5. Thus, thecirculation gate CG1 may correspond to a gate of the circulationtransistor CX1, the circulation gate CG2 may correspond to a gate of thecirculation transistor CX2, the circulation gate CG3 may correspond to agate of the circulation transistor CX3, and the circulation gate CG4 maycorrespond to a gate of the circulation transistor CX4. In addition, thedrain nodes D1˜D4 may respectively correspond to terminals of thecirculation transistors CX1˜CX4 each receiving the drain voltage (Vd) asan input. In more detail, the drain node D1 may correspond to a terminalof the circulation transistor CX1 receiving the drain voltage (Vd), thedrain node D2 may correspond to a terminal of the circulation transistorCX2 receiving the drain voltage (Vd), the drain node D3 may correspondto a terminal of the circulation transistor CX3 receiving the drainvoltage (Vd), and the drain node D4 may correspond to a terminal of thecirculation transistor CX4 receiving the drain voltage (Vd).

The photoelectric conversion element PD may be formed in a semiconductorsubstrate, and may be surrounded by the plurality of gates TG1˜TG4 andCG1˜CG4.

Each of the floating diffusion (FD) regions FD1˜FD4 may be located atone side of each of the transfer gates TG1˜TG4 corresponding thereto. Inmore detail, the floating diffusion (FD) region FD1 may be located atone side of the transfer gate TG1, the floating diffusion (FD) regionFD2 may be located at one side of the transfer gate TG2, the floatingdiffusion (FD) region FD3 may be located at one side of the transfergate TG3, and the floating diffusion (FD) region FD4 may be located atone side of the transfer gate TG4. Signals corresponding to the amountof photocharges stored in the floating diffusion (FD) regions FD1˜FD4may be respectively output as tap signals TAP1˜TAP4 corresponding to thefloating diffusion (FD) regions FD1˜FD4. In more detail, a signalcorresponding to the amount of photocharges stored in the floatingdiffusion (FD) region FD1 may be output as a tap signal TAP1, a signalcorresponding to the amount of photocharges stored in the floatingdiffusion (FD) region FD2 may be output as a tap signal TAP2, a signalcorresponding to the amount of photocharges stored in the floatingdiffusion (FD) region FD3 may be output as a tap signal TAP3, and asignal corresponding to the amount of photocharges stored in thefloating diffusion (FD) region FD4 may be output as a tap signal TAP4.The tap signals TAP1˜TAP4 may be respectively applied to gates of thedrive transistors DX1˜DX4 corresponding thereto through conductivelines. In addition, the tap signals TAP1˜TAP4 may be respectivelyapplied to terminals of the reset transistors RX1˜RX4 correspondingthereto through conductive lines. Each of the floating diffusion (FD)regions FD1˜FD4 may include an impurity region that is formed byimplanting N-type impurities into a semiconductor substrate to apredetermined depth.

The drain nodes D1˜D4 may be respectively located at one sides of thecirculation gates CG1˜CG4 corresponding thereto, and may be coupled tothe drain voltage (Vd) through conductive lines. Each of the drain nodesD1˜D4 may include an impurity region that is formed by implanting N-typeimpurities into a semiconductor substrate to a predetermined depth.

The transfer gates TG1˜TG4 may be respectively arranged at differentpositions corresponding to vertex points of a rectangular ring shapesurrounding the photoelectric conversion element PD.

The circulation gates CG1˜CG4 may be respectively disposed in regionscorresponding to four sides of the rectangular ring shape surroundingthe photoelectric conversion element PD. During the modulation period,the circulation gates CG1˜CG4 may sequentially and consecutively receivecirculation control voltages Vcir1˜Vcir4 in a predetermined direction(for example, a counterclockwise direction), such that the circulationgates CG1˜CG4 may partially generate an electric field in an edge regionof the photoelectric conversion element PD and may enable the electricfield to be changed along the corresponding direction at intervals of apredetermined time. Photocharges stored in the photoelectric conversionelement PD may move from one place to another place in the direction inwhich the electric field is generated and changed.

In this case, each of the circulation control voltages Vcir1˜Vcir4 mayhave a potential level that is unable to electrically connect thephotoelectric conversion element PD to each of the drain nodes D1˜D4.Thus, during the modulation period, the circulation gates CG1˜CG4 maynot turn on the circulation transistors CX1˜CX4 corresponding thereto,and may perform only the role of moving photocharges of thephotoelectric conversion element PD.

During the readout period, each of the circulation gates CG1˜CG4 may fixa voltage level of the photoelectric conversion element PD to the drainvoltage (Vd) by the draining control voltage (Vdrain), such that thecirculation gates CG1˜CG4 can prevent noise from flowing into thephotoelectric conversion element PD, resulting in no signal distortion.For example, when the draining control voltage (Vdrain) is activated toa logic high level, each of the circulation gates (CG1˜CG4) may have ahigh potential that can electrically connect the photoelectricconversion element PD to each of the drain nodes D1˜D4. Thus, theactivated draining control voltage (Vdrain) may have a higher voltagethan each of the activated circulation control voltages Vcir1˜Vcir4.

Accordingly, during the readout period, the draining control voltage(Vdrain) may be activated to a logic high level. In this case, sinceeach of the drain nodes D1˜D4 is electrically coupled to thephotoelectric conversion element PD, the photoelectric conversionelement PD may be fixed to a high drain voltage (Vd), such that residualphotocharges in the photoelectric conversion element PD can be drained.

The circulation gate CG1 may receive the circulation control signal CXV1that corresponds to either the circulation control voltage (Vcir1) orthe draining control voltage (Vdrain) based on the switching operationof the switching element S1 corresponding to the circulation gate CG1.The circulation gate CG2 may receive the circulation control signal CXV2that corresponds to either the circulation control voltage (Vcir2) orthe draining control voltage (Vdrain) based on the switching operationof the switching element S2 corresponding to the circulation gate CG2.The circulation gate CG3 may receive the circulation control signal CXV3that corresponds to either the circulation control voltage (Vcir3) orthe draining control voltage (Vdrain) based on the switching operationof the switching element S3 corresponding to the circulation gate CG3.The circulation gate CG4 may receive the circulation control signal CXV4that corresponds to either the circulation control voltage (Vcir4) orthe draining control voltage (Vdrain) based on the switching operationof the switching element S4 corresponding to the circulation gate CG4.In more detail, during the modulation period, the circulation gatesCG1˜CG4 may respectively receive the circulation control voltagesVcir1˜Vcir4. During the readout period, each of the circulation gatesCG1˜CG4 may receive the draining control voltage (Vdrain). Although theswitching elements S1˜S4 may be included in the pixel driver 130, otherimplementations are also possible.

The transfer gates TG1˜TG4 and the circulation gates CG1˜CG4 may bespaced apart from each other by a predetermined distance while beingarranged alternately with each other over the semiconductor substrate.When viewed in a plane, the transfer gates TG1˜TG4 and the circulationgates CG1˜CG4 may be arranged in a ring shape that surrounds thephotoelectric conversion element PD.

The circulation gates CG1 and CG3 may be respectively arranged at bothsides of the photoelectric conversion element PD in a first directionwith respect to the photoelectric conversion element PD at an upperportion of the semiconductor substrate. The circulation gates CG2 andCG4 may be respectively arranged at both sides of the photoelectricconversion element PD in a second direction with respect to thephotoelectric conversion element PD. For example, the circulation gatesCG1˜CG4 may be respectively disposed in regions corresponding to foursides of the rectangular ring shape surrounding the photoelectricconversion element PD. In this case, the circulation gates CG1˜CG4 maybe arranged to partially overlap with the photoelectric conversionelement PD

On the other hand, each of the transfer gates TG1˜TG4 may be spacedapart from two contiguous or adjacent circulation gates by apredetermined distance, and may be disposed between the two contiguousor adjacent circulation gates. For example, the transfer gates TG1˜TG4may be disposed in regions corresponding to vertex points of therectangular ring shape, and may be arranged to partially overlap withthe photoelectric conversion element PD.

FIG. 7 illustrates moves of photocharges by the circulation gatesCG1˜CG4 in the indirect pixel shown in FIG. 6 based on someimplementations of the disclosed technology.

Referring to FIG. 7, when the circulation control voltages Vcir1˜Vcir4are respectively applied to the circulation gates CG1˜CG4, the electricfield may be formed in a peripheral region of the circulation gatesCG1˜CG4, such that photocharges generated by the photoelectricconversion element PD may move from the edge region of the photoelectricconversion element PD to another region contiguous or adjacent to thecirculation gates CG1˜CG4. In this case, when the potential of each ofthe circulation control voltages Vcir1˜Vcir4 is less than apredetermined potential that can create a channel capable ofelectrically coupling the photoelectric conversion element PD to each ofthe drain nodes D1˜D4, photocharges can be accumulated or collected inthe peripheral region of the circulation gates CG1˜CG4 without moving tothe drain nodes D1˜D4.

However, as can be seen from FIG. 6, the circulation gates CG1˜CG4 aredisposed to surround the upper portion of the photoelectric conversionelement PD. The circulation control voltages Vcir1˜Vcir4 are not appliedsimultaneously, but are sequentially and consecutively applied to thecirculation gates CG1˜CG4 in a predetermined direction (for example, acounterclockwise direction), and thus photocharges may move along theedge region of the photoelectric conversion element PD according to adesired sequence of operations of the circulation gates CG1˜CG4. Assuch, photocharges can move in a predetermined direction along the edgeregion of the photoelectric conversion element PD.

In some implementations, at a first point in time, the circulationcontrol signal (Vcir1) is applied to the circulation gate CG1 and thusthe electric field is formed in the peripheral region of the circulationgate CG1. In this case, photocharges generated by the photoelectricconversion element PD can be accumulated near the circulation gate CG1by the electric field.

After a predetermined time period, at a second point in time, thecirculation control signal (Vcir2) is applied to the circulation gateCG2 contiguous or adjacent to the circulation gate CG1, and thecirculation control signal (Vcir1) ceases to be applied to thecirculation gate CG1. Thus, photocharges accumulated near thecirculation gate CG1 may move toward the circulation gate CG2. Thus,photocharges may move from the circulation gate CG1 to the circulationgate CG2.

After a predetermined time period, at a third point in time, thecirculation control signal (Vcir3) is applied to the circulation gateCG3 contiguous or adjacent to the circulation gate CG2, and thecirculation control signal (Vcir2) ceases to be applied to thecirculation gate CG2. Thus, photocharges accumulated near thecirculation gate CG2 may move toward the circulation gate CG3. Thus,photocharges may move from the circulation gate CG2 to the circulationgate CG3.

After a predetermined time period, at a fourth point in time, thecirculation control signal (Vcir4) is applied to the circulation gateCG4 contiguous or adjacent to the circulation gate CG3, and thecirculation control signal (Vcir3) ceases to be applied to thecirculation gate CG3. Thus, photocharges accumulated near thecirculation gate CG3 may move toward the circulation gate CG4. Thus,photocharges may move from the circulation gate CG3 to the circulationgate CG4.

After a predetermined time period, at a fifth point in time, thecirculation control signal (Vcir1) is applied to the circulation gateCG1 contiguous or adjacent to the circulation gate CG4, and thecirculation control signal (Vcir4) ceases to be applied to thecirculation gate CG4. Thus, photocharges accumulated near thecirculation gate CG4 may move toward the circulation gate CG1. Thus,photocharges may move from the circulation gate CG4 to the circulationgate CG1.

If the above-mentioned operations are consecutively and repeatedlycarried out, photocharges can be circulated along the edge region of thephotoelectric conversion element (PD).

FIG. 8 is a conceptual diagram illustrating how photocharges are movingtoward a floating diffusion (FD) region by transfer gates in theindirect pixel shown in FIG. 6 based on some implementations of thedisclosed technology. FIG. 8 illustrates how the indirect pixel shown inFIG. 6 transfers photocharges to the floating diffusion (FD) region bytransfer gates.

Referring to FIG. 8, in some implementations, when the transfer controlsignals TFv1˜TFv4 are respectively applied to the transfer gatesTG1˜TG4, an electrical channel is created in the semiconductor substratebelow the transfer gates TG1˜TG4 to couple the photoelectric conversionelement (PD) to the floating diffusion (FD) regions FD1˜FD4. Thephotocharges generated by the photoelectric conversion element (PD) canbe transferred to the floating diffusion (FD) regions FD1˜FD4 throughthe channel.

The transfer control signals TFv1˜TFv4 are not applied simultaneously,but are sequentially and consecutively applied to the transfer gatesTG1˜TG4 in a predetermined direction (for example, a counterclockwisedirection). The transfer control signals TFv1˜TFv4 may be sequentiallyapplied to the transfer gates TG1˜TG4 according to a desired sequence ofoperations of the circulation gates CG1˜CG4 shown in FIG. 7.

For example, in a situation in which photocharges accumulated near thecirculation gate CG1, by activation of the circulation gate CG1, movetoward the circulation gate CG2, the transfer control signal (TFv1) canbe applied only to the transfer gate TG1 located between the circulationgates CG1 and CG2. In this case, the transfer control signal (TFv1) mayhave a higher voltage than each of the circulation control voltagesVcir1 and Vcir2.

As described above, in the arrangement structure in which the transfergate TG1 and the circulation gates CG1 and CG2 are arranged in anL-shape structure, in a situation in which the transfer gate TG1 islocated at a vertex position and at the same time the signal (TFv1)applied to the transfer gate TG1 is at a higher voltage level than eachof the signals Vcir1 and Vcir2 applied to the circulation gates CG1 andCG2, most parts of photocharges collected by the circulation gates CG1and CG2 and the transfer gate TG1 may be intensively collected in theregion located close to the transfer gate TG1. That is, most parts ofthe collected photocharges may be concentrated in a narrow region.Therefore, even when the transfer gate TG1 having a relatively smallsize is used, photocharges can be rapidly transferred to the floatingdiffusion (FD) region FD1.

In the same manner as described above, in a situation in whichphotocharges accumulated near the circulation gate CG2 move toward thecirculation gate CG3, the transfer control signal (TFv2) can be appliedonly to the transfer gate TG2 located between the circulation gates CG2and CG3. In addition, if photocharges accumulated near the circulationgate CG3 move toward the circulation gate CG4, the transfer controlsignal (TFv3) can be applied only to the transfer gate TG3 locatedbetween the circulation gates CG3 and CG4. Likewise, if photochargesaccumulated near the circulation gate CG4 move toward the circulationgate CG1, the transfer control signal (TFv4) can be applied only to thetransfer gate TG4 located between the circulation gates CG4 and CG1.

FIG. 9 is a timing diagram illustrating an example of operations of theimage sensing device 100 based on some implementations of the disclosedtechnology.

Referring to FIG. 9, the operation period of the image sensing device100 may be broadly classified into a modulation period and a readoutperiod.

The modulation period may refer to a time period in which the lightsource 10 emits light to a target object 1 under control of the lightsource driver 170 and senses light reflected from the target object 1using the direct TOF method or the indirect TOF method.

The readout period may refer to a time period in which the pixel signalgeneration circuits PGC1˜PGC4 of the indirect pixel (IPX) mayrespectively read the tap signals TAP1˜TAP4 corresponding to the amountof photocharges accumulated in the floating diffusion (FD) regionsFD1˜FD4 during the modulation section, may generate indirect pixeloutput signals IPXout1˜IPXout4 based on the read tap signals TAP1˜TAP4,and may thus generate digital data corresponding to the indirect pixeloutput signals IPXout1˜IPXout4. In this case, a direct pixel outputsignal (DPXout) of the direct pixel (DPX) and digital data correspondingto the direct pixel output signal (DPXout) may be immediately generatedas soon as the direct pixel (DPX) senses light, such that the directpixel output signal (DPXout) and the digital data corresponding theretocan be transferred to the image signal processor 200 in real time. Thus,the readout period may refer to a time period in which the indirectpixel output signals IPXout1˜IPXout4 of the indirect pixel (IPX) anddigital data corresponding thereto are generated and transferred.

If the readout enable signal (ROUTen) is deactivated to a logic lowlevel at a time point (t1), the modulation period may start operation.If the modulation period starts operation, the image sensing device 100may operate in the object monitoring mode by default, and may generatedigital data indicating the distance to the target object using thedirect TOF method. In more detail, a direct TOF enable signal (dToFen)may be activated to a logic high level at the time point (t1). Thereadout enable signal (ROUTen), the direct TOF enable signal (dToFen),and an indirect TOF enable signal (iToFen) to be described later may begenerated by the image signal processor 200, and may thus be transferredto the image sensing device 100.

The image sensing device 100 may repeatedly emit pulse lightsynchronized with the clock signal (MLS) to the target object 1 atintervals of a predetermined time (for example, t1˜t2 or t2˜t3). Thepulse light may be denoted by “LIGHT” as shown in FIG. 9.

In addition, FIG. 9 illustrates an event signal (EVENT) acting as thedirect pixel output signal (DPXout) that is generated when light emittedfrom the image sensing device 100 is sensed after being reflected fromthe target object 1. In other words, the event signal (EVENT) may referto the direct pixel output signal (DPXout) that is generated by sensinglight reflected from the target object 1.

On the other hand, FIG. 9 illustrates a signal (DARK) acting as a directpixel output signal (DPXout) that is generated when a dark noisecomponent (e.g., ambient noise) irrelevant to light emitted from theimage sensing device 100 is sensed and generated. That is, the signal(DARK) may refer to the direct pixel output signal (DPXout) that isgenerated by sensing the dark noise component instead of light reflectedfrom the target object 1.

Light emitted from the image sensing device 100 at the time points t1and t2 may be reflected by the target object 1, and the reflected lightmay be sensed, such that the signal (EVENT) may be generated. However, adistance corresponding to a time delay between the signal (LIGHT) andthe signal (EVENT) may exceed a threshold distance, and the countedresultant value stored in the mode counter of the image signal processor200 may not increase.

On the other hand, the signal (DARK) may occur due to the dark noisecomponent in a time period t2˜t3. The distance corresponding to a timedelay between the signal (LIGHT) and the signal (DARK) may be equal toor less than a threshold distance, and the counted resultant valuestored in the mode counter may increase. However, since the countedresultant value does not exceed a mode switching value, switching of theoperation mode of the image sensing device 100 may not occur.

Light emitted from the image sensing device 100 at each of the timepoints t4, t5, and t6 may be sensed after being reflected from thetarget object 1, such that the signal (EVENT) may occur. The distancecorresponding to the time delay between the signal (LIGHT) and thesignal (EVENT) may be equal to or less than a threshold distance, andthe counted resultant value stored in the mode counter may increase.

Meanwhile, in a time period t4˜t7, the signal (DARK) may occur twice dueto the dark noise component. The distance corresponding to the timedelay between the signal (LIGHT) and the signal (DARK) may exceed or belonger than the threshold distance, and the counted resultant valuestored in the mode counter may not increase.

However, assuming that the counted resultant value does not exceed themode switching value at the time point (t7), switching of the operationmode of the image sensing device 100 may not occur.

That is, if each of the threshold distance, the mode switching value,and the initialization time is set to an appropriate value, erroneousincrease of the counted resultant value or erroneous switching of theoperation mode may be prevented by the signal DARK. Although each of thethreshold distance, the mode switching value, and the initializationtime can be experimentally determined in advance, the scope or spirit ofthe disclosed technology is not limited thereto, and otherimplementations are also possible. In some implementations, the imagesignal processor 200 may also dynamically change at least one of thethreshold distance, the mode switching value, and the initializationvalue according to external conditions (e.g., illuminance outside thephotographing device, speed of the photographing device, a user request,etc.).

Light emitted from the image sensing device 100 at a time point (t8) maybe sensed after being reflected from the target object 1, such that thesignal (EVENT) may occur. The distance between the time delay betweenthe signal (LIGHT) and the signal (EVENT) may be equal to or less than athreshold distance, and the counted resultant value stored in the modecounter may increase. Assuming that the counted resultant value exceedsor is higher than the mode switching value at the time point (t8), theimage signal processor 200 may allow the operation mode of the imagesensing device 100 to switch from the object monitoring mode to thedepth resolving mode.

Therefore, at a time point (t9), the direct TOF enable signal (dToFen)may be deactivated to a logic low level, and the indirect TOF enablesignal (iToFen) may be activated to a logic high level. Accordingly, theimage sensing device 100 may generate digital data indicating thedistance to the target object 1 using the indirect TOF method.

During the depth resolving mode after the time point (t9), the imagesensing device 100 may repeatedly emit a modulated light synchronizedwith the clock signal (MLS) to the target object 1 at intervals of apredetermined time (for example, t10˜t15).

In the modulation period, the drain voltage (Vd) applied to each of thedrain nodes D1˜D4 may be at a low-voltage (e.g., a ground voltage)level. In the readout period, the drain voltage (Vd) applied to each ofthe drain nodes D1˜D4 may be at a high-voltage (e.g., a power-supplyvoltage) level. For example, if the drain voltage (Vd) is at ahigh-voltage level even in the modulation period, the drain voltage (Vd)may prevent photocharges collected by the circulation gates from movingtoward the transfer gate. Therefore the drain voltage (Vd) may bemaintained at a low-level level in the modulation period.

At a time point (t9) where the depth resolving mode is started, thecirculation control voltage (Vcir1) may be activated. That is, thecirculation control voltage (Vcir1) may be applied to the circulationgate CG1 at the time point (t9). In this case, the circulation controlvoltage (Vcir1) may have a potential level that is unable toelectrically connect the photoelectric conversion element PD to thedrain node D1. The circulation control voltage (Vcir1) may be activatedduring a time period t9˜t11.

Since the activated circulation control voltage (Vcir1) is applied tothe circulation gate CG1, the electric field may be formed in a regionthat is contiguous or adjacent to the circulation gate CG1 in the edgeregion of the photoelectric conversion element PD. As a result,photocharges generated by photoelectric conversion of reflected light inthe photoelectric conversion element (PD) may move toward thecirculation gate CG1 by the electric field, such that the resultantphotocharges are accumulated near or collected in the circulation gateCG1.

At a time point (t10), the transfer control signal (TFv1) and thecirculation control voltage (Vcir2) may be activated. For example, inthe situation in which the circulation control signal (Vcir1) is stillactivated, if the circulation control signal (Vcir2) is applied to thecirculation gate CG2 and at the same time the transfer control signal(TFv1) is applied to the transfer gate TG1, the circulation gates CG1and CG2 and the transfer gate TG1 can operate at the same time. In thiscase, the transfer control signal (TFv1) may have a higher voltage thaneach of the circulation control voltages Vcir1 and Vcir2. The transfercontrol signal (TFv1) may be activated during a time period t10˜t11, andthe circulation control voltage (Vcir2) may be activated during a timeperiod t10˜t12.

Therefore, photocharges collected near the circulation gate CG1 duringthe time period t10˜t11 may move toward the transfer gate TG1. Inaddition, photocharges additionally collected by the transfer gate TG1and the circulation gates CG1 and CG2 during the time period t11˜t12 mayalso move toward the transfer gate TG1.

Whereas the circulation gates CG1 and CG2 and the transfer gate TG1 arearranged in an L-shape structure, the transfer gate TG1 is arranged at avertex position and a relatively higher potential is applied to thetransfer gate TG1, such that photocharges can be intensively collectedin the region (i.e., the vertex region) located close to the transfergate TG1.

The collected photocharges can be transferred to the floating diffusion(FD) region FD1 by the transfer gate TG1. Thus, photocharges areintensively collected in a narrow vertex region, such that photochargescan be rapidly transferred to the floating diffusion (FD) region FD1using a small-sized transfer gate TG1.

At the time point (t11), the circulation control signal (Vcir1) and thetransfer control signal (TFv1) may be deactivated, and the transfercontrol signal (TFv2) and the circulation control signal (Vcir3) may beactivated. Thus, the transfer gate TG1 and the circulation gate CG1 thatare located at one side of the circulation gate CG2 may stop operation,and the transfer gate TG2 and the circulation gate CG3 that are locatedat the other side of the circulation gate CG2 may start operation. Inthis case, the activated transfer control signal (TFv2) may have ahigher voltage than the circulation control voltage (Vcir3).

However, although the transfer control signal (TFv2) and the circulationcontrol signal (Vcir3) are activated, a predetermined time (i.e., arising time) may be consumed until the potential levels of the transfercontrol signal (TFv2) and the circulation control voltage (Vcir3) reacha predetermined level at which the gates TG2 and CG3 can actuallyoperate. Thus, there may occur a time period in which the transfer gateTG1 stops operation and the transfer gate TG2 is not yet operated.

Therefore, the circulation control signal (Vcir2) is continuouslyactivated until reaching the time point (t12). As a result, during apredetermined time in which the transfer gate TG2 is not yet operated,photocharges may not be dispersed and move toward the circulation gateCG2. For example, not only photocharges not transferred by the transfergate TG1, but also newly generated photocharges may move toward thecirculation gate CG2.

If the rising time of each of the transfer control signal (TFv2) and thecirculation control voltage (Vcir3) has expired, the transfer gate TG2may operate by the transfer control signal (TFv2) and the circulationgate CG3 may operate by the circulation control signal (Vcir3). Thus,the circulation gates CG2 and CG3 and the transfer gate TG2 may operateat the same time. In this case, since the transfer control signal (TFv2)has a higher voltage than each of the circulation control voltages Vcir2and Vcir3, photocharges may move toward the transfer gate TG2 and mayflow into the floating diffusion (FD) region FD2 by the transfer gateTG2.

At the time point (t12), the circulation control signal (Vcir2) and thetransfer control signal (TFv2) may be deactivated, and the transfercontrol signal (TFv3) and the circulation control signal (Vcir4) may beactivated. Thus, the transfer gate TG2 and the circulation gate CG2 thatare located at one side of the circulation gate CG3 may stop operation,and the transfer gate TG3 and the circulation gate CG4 that are locatedat the other side of the circulation gate CG3 may start operation. Inthis case, the transfer control signal (TFv3) may have a higher voltagethan the circulation control voltage (Vcir4).

In this case, the circulation control voltage (Vcir3) is continuouslyactivated until reaching the time point (t13). As a result, during apredetermined time in which the transfer gate TG3 is not yet operated,photocharges may not be dispersed and move toward the circulation gateCG3.

If the rising time of each of the transfer control signal (TFv3) and thecirculation control voltage (Vcir4) has expired, the transfer gate TG3may operate by the transfer control signal (TFv3) and the circulationgate CG4 may operate by the circulation control voltage (Vcir4). Thus,the circulation gates CG3 and CG4 and the transfer gate TG3 may operateat the same time. In this case, since the transfer control signal (TFv3)has a higher voltage than each of the circulation control voltages Vcir3and Vcir4, photocharges may move toward the transfer gate TG3 and mayflow into the floating diffusion (FD) region FD3 by the transfer gateTG3.

At a time point (t13), the circulation control signal (Vcir3) and thetransfer control signal (TFv3) may be deactivated, and the transfercontrol signal (TFv4) may be activated. In this case, the activatedtransfer control signal (TFv4) may have a higher voltage than thecirculation control voltage (Vcir4), and the circulation control signal(Vcir4) may remain activated until reaching the time point (t14).

Therefore, photocharges may move toward the circulation gate CG4.Thereafter, if the rising time of the transfer control signal (TFv4) hasexpired, photocharges may flow into the floating diffusion (FD) regionFD4 by the transfer gate TG4.

The time period t9˜t14 may be defined as a first indirect cycle. Untilthe modulation period is ended, the operation of moving photocharges andthe operation of sequentially transferring the moved photocharges to thefloating diffusion (FD) regions FD1˜FD4 may be repeatedly performed inthe same manner as in the time period t9˜t14. As can be seen from FIG.9, the operation corresponding to the first indirect cycle from amongthe second to m-th indirect cycles (where ‘m’ is an integer of 3 ormore) may be repeatedly performed. As a result, although photoelectricconversion sensitivity of the photoelectric conversion element PD is ata low level or transmission (Tx) efficiency of the transfer gatesTG1˜TG4 is at a low level, the accuracy of sensing the distance to thetarget object using the indirect TOF method can be increased orimproved. Information about how many times the first indirect cycle isrepeated may be experimentally determined in advance in consideration ofphotoelectric conversion sensitivity of the photoelectric conversionelement PD or transmission (Tx) efficiency of the transfer gatesTG1˜TG4. In some other implementations, the first indirect cycle may notbe repeated, and the readout period may be started as soon as the firstindirect cycle is ended.

If the modulation period has expired, the readout enable signal (ROUTen)is activated such that the readout period may be started. In this case,the drain voltage (Vd) may be activated to a high-voltage level, and thedraining control signal (Vdrain) may also be activated to a high-voltagelevel. Therefore, the photoelectric conversion element PD may beelectrically coupled to the drain nodes D1˜D4 by the circulation gatesCG1˜CG4, such that the voltage level of the photoelectric conversionelement PD may be fixed to the drain voltage (Vd) during the readoutperiod.

FIG. 10 is a schematic diagram illustrating an example of someconstituent elements included in the image sensing device shown in FIG.1 based on some implementations of the disclosed technology.

Referring to FIG. 10, the image sensing device 1000 may illustrate oneexample of some constituent elements included in the image sensingdevice 100 shown in FIG. 1. The image sensing device 1000 may include apixel array 1005, a row driver 1050, a modulation driver 1060, ahorizontal time-to-digital circuit (TDC) 1070, a vertical TDC 1080, andan indirect readout circuit 1090.

The pixel array 1005 may correspond to the pixel array 110 shown in FIG.1, and may include a plurality of direct pixels 1010 and a plurality ofindirect pixels 1040. Although the pixel array 1005 shown in FIG. 10based on some implementations of the disclosed technology may include aplurality of pixels arranged in a matrix shape including desired numbersof rows and columns, e.g., 22 rows and 22 columns. In implementations,the number of rows and the number of columns included in the pixel array1005 may be set as needed. Since the number of rows and the number ofcolumns are determined based on the indirect pixel 1040, the directpixel different in size from the indirect pixel 1040 may be arrangedacross two rows and two columns.

The plurality of direct pixels 1010 may be included in a first directpixel group 1020 and/or a second direct pixel group 1030. Although eachdirect pixel 1010 may be four times larger than each indirect pixel1040, the scope or spirit of the disclosed technology is not limitedthereto, and other implementations are also possible. This is becausethe quenching circuit (QC) or the recharging circuit (RC) included inthe direct pixel 1010 may be relatively large in size. In some otherimplementations, the ratio in size between the direct pixel 1010 and theindirect pixel 1040 may be set to a desired ratio for a specific design,for example, “1”, “½”, “ 1/16”, or other ratios.

The first direct pixel group 1020 may include a plurality of directpixels 1010 arranged in a line in a first diagonal direction of thepixel array 1005. For example, the first diagonal direction may refer toa straight direction by which a first crossing point where the first rowand the first column of the pixel array 1005 cross each other isconnected to a second crossing point where the last row and the lastcolumn of the pixel array 1005 cross each other.

The second direct pixel group 1030 may include a plurality of directpixels 1010 arranged in a line in a second diagonal direction of thepixel array 1005. For example, the second diagonal direction may referto a straight direction by which a first crossing point where the firstrow and the last column of the pixel array 1005 cross each other isconnected to a second crossing point where the last row and the firstcolumn of the pixel array 1005 cross each other.

A central pixel disposed at a crossing point of the first direct pixelgroup 1020 and the second direct pixel group 1030 may be included ineach of the first direct pixel group 1020 and the second direct pixelgroup 1030.

The direct pixels 1010 may be arranged in a line sensor shape within thepixel array 1005, such that the entire region including the directpixels 1010 arranged in the line sensor shape may be smaller in sizethan the region including the indirect pixels 1040. This is because thedirect pixels 1010 are designed to have a relatively longer effectivemeasurement distance and a relatively higher temporal resolution ratherthan a purpose of acquiring an accurate depth image. As a result, thedirect pixels 1010 can recognize the presence or absence of the targetobject 1 in the object monitoring mode using the relatively longereffective measurement distance and the relatively higher temporalresolution, and at the same time can correctly measure the distance tothe target object 1 using the relatively longer effective measurementdistance and the relatively higher temporal resolution.

Meanwhile, when viewed from depth images respectively generated by theindirect pixels 1040, each of the direct pixels 1010 may act as a deadpixel. In this case, the image signal processor 200 may performinterpolation of the depth images respectively corresponding topositions of the direct pixels 1010, by means of digital data of theindirect pixels 1040 that are located adjacent to the direct pixels 1010within the range of a predetermined distance (e.g., two pixels) or less.

In the rectangular pixel array 1005, the plurality of indirect pixels1040 may be arranged in a matrix shape within the remaining regionsother than the region provided with the plurality of direct pixels 1010.

The row driver 1050 and the modulation driver 1060 may correspond to theindirect pixel driver 130 shown in FIG. 1. The row driver 1050 may bearranged in a vertical direction (or a column direction) of the pixelarray 1005, and the modulation driver 1060 may be arranged in ahorizontal direction (or a row direction) of the pixel array 1005.

The row driver 1050 may provide the reset control signals RG1˜RG4 andthe selection control signals SEL1˜SEL4 to each of the indirect pixels1040. The reset control signals RG1˜RG4 and the selection controlsignals SEL1˜SEL4 may be supplied through a signal line extending in ahorizontal direction, such that the plurality of indirect pixels 1040belonging to the same row of the pixel array 1005 may receive the samereset control signals RG1˜RG4 and the same selection control signalsSEL1˜SEL4.

The modulation driver 1060 may provide the circulation control signalsCXV1˜CXV4 and the transfer control signals TFv1˜TFv4 to each of theindirect pixels 1040. The circulation control signals CXV1˜CXV4 and thetransfer control signals TFv1˜TFv4 may be supplied through a signal lineextending in a vertical direction, such that the plurality of indirectpixels 1040 belonging to the same column of the pixel array 1005 mayreceive the same circulation control signals CXV1˜CXV4 and the sametransfer control signals TFv1˜TFv4.

Although not shown in FIG. 10, if at least one of the quenching circuit(QC) and the recharging circuit (RC) in each of the direct pixels 1010is implemented as an active device, the direct pixel driver forsupplying the quenching control signal (QCS) and/or the rechargingcontrol signal may be further disposed. A method for supplying signalsby the direct pixel driver may correspond to that of the row driver1050.

The horizontal TDC 1070 and the vertical TDC 1080 may correspond to thedirect readout circuit 140 shown in FIG. 1. The horizontal TDC 1070 maybe arranged in a horizontal direction (or a row direction) at an upperside (or a lower side) of the pixel array 1005. The vertical TDC 1080may be arranged in a vertical direction (or a column direction) at aright side (or a left side) of the pixel array 1005.

The horizontal TDC 1070 may be coupled to each direct pixel 1010included in the first direct pixel group 1020. The horizontal TDC 1070may include a plurality of TDCs (i.e., TDC circuits) that correspond tothe direct pixels 1010 of the first direct pixel group 1020 on a one toone basis.

The vertical TDC 1080 may be coupled to each direct pixel 1010 includedin the second direct pixel group 1030. The vertical TDC 1080 may includea plurality of TDCs (i.e., TDC circuits) that correspond to the directpixels 1010 of the second pixel group 1030 on a one to one basis.

Each TDC included in either the horizontal TDC 1070 or the vertical TDC1080 may include a digital logic circuit configured to generate digitaldata by calculating a time delay between a pulse signal of thecorresponding direct pixel DPX and a reference pulse, and an outputbuffer configured to store the generated digital data therein. The pointof each direct pixel 1010 shown in FIG. 10 may refer to a terminal forelectrical connection to either the horizontal TDC 1070 or the verticalTDC 1080. The central pixel may include two points, such that the twopoints may be respectively coupled to the horizontal TDC 1070 and thevertical TDC 1080.

In the image sensing device 1000 based on some implementations of thedisclosed technology, each TDC circuit may not be disposed in the directpixel 1010, and may be disposed at one side of the pixel array 1005without being disposed in the pixel array 1005, such that the region ofeach direct pixel 1010 can be greatly reduced in size. Accordingly, thedirect pixels 1010 and the indirect pixels 1040 may be simultaneouslydisposed in the pixel array 1005, and many more direct pixels 1010 canbe disposed in the pixel array 1005, such that higher resolution may beobtained when the distance to the target object is sensed by the directTOF method.

The indirect readout circuit 1090 may correspond to the indirect readoutcircuit 150 shown in FIG. 1, may process analog pixel signals generatedfrom the indirect pixels 1040, may generate and store digital datacorresponding to the processed pixel signals. The indirect pixels 1040belonging to the same column of the pixel array 1005 may output pixelsignals through the same signal line. Therefore, in order to normallytransfer such pixel signals, the indirect pixels 1040 may sequentiallyoutput the pixel signals on a row basis.

FIG. 11 is a conceptual diagram illustrating an example of operations ofthe image sensing device 1000 shown in FIG. 10 based on someimplementations of the disclosed technology.

Referring to FIGS. 10 and 11, when the image sensing device 1000operates in each of the object monitoring mode and the depth resolvingmode, information about how pixels are activated according to lapse oftime are illustrated. In this case, activation of such pixels may referto an operation state in which each pixel receives a control signal fromthe corresponding pixel driver 120 or 130, generates a signal (e.g., apulse signal or a pixel signal) formed by detection of incident light,and transmits the generated signal to the corresponding readout circuit140 or 150. In FIG. 11, the activated pixels may be represented byshaded pixels.

In the object monitoring mode in which the image sensing device 1000generates digital data indicating the distance to the target objectusing the direct TOF method, the image sensing device 1000 may operatesequentially in units of a direct cycle (or on a direct-cycle basis). Ascan be seen from FIG. 11, the image sensing device 1000 may sequentiallyoperate in the order of first to twelfth direct cycles DC1˜DC12. Each ofthe first to twelfth direct cycles DC1˜DC12 may refer to a time periodin which a series of operations including, for example, an operation ofemitting pulse light to the target object 1, an operation of generatinga pulse signal corresponding to reflected light received from the targetobject 1, an operation of generating digital data corresponding to thepulse signal, a quenching operation, and a recharging operation, can beperformed. For example, the time period t1˜t2 or t2˜t3 shown in FIG. 9may correspond to a single direct cycle.

In the first direct cycle DC1, the direct pixels 1010 included in thefirst direct pixel group 1020 may be activated, and the direct pixels1010 included in the second direct pixel group 1030 may be deactivated.The horizontal TDC 1070 for processing the pulse signal of the firstdirect pixel group 1020 may be activated, and the vertical TDC 1080 forprocessing the pulse signal of the second direct pixel group 1030 may bedeactivated. In addition, the indirect pixels 1040, and the constituentelements 1050, 1060, and 1090 for controlling and reading out theindirect pixels 1040 may be deactivated.

In the second direct cycle DC2, the direct pixels 1010 included in thefirst direct pixel group 1020 may be deactivated, and the direct pixels1010 included in the second direct pixel group 1030 may be activated. Inaddition, the horizontal TDC 1070 for processing the pulse signal of thefirst direct pixel group 1020 may be deactivated, and the vertical TDC1080 for processing the pulse signal of the second direct pixel group1030 may be activated. In addition, the indirect pixels 1040, and theconstituent elements 1050, 1060, and 1090 for controlling and readingout the indirect pixels 1040 may be deactivated.

Not only in the third to twelfth direct cycles DC3˜DC12, but also insubsequent direct cycles, the direct pixels 1010 included in the firstdirect pixel group 1020 and the direct pixels included in the seconddirect pixel group 1030 may be alternately activated in the same manneras in the first direct cycle DC1 and the second direct cycle DC2.Therefore, the horizontal TDC 1070 and the vertical TDC 1080 may also beactivated alternately with each other.

Therefore, a minimum number of the direct pixels having relatively largepower consumption may be included in the pixel array 1005, and only someof the direct pixels may be activated within one direct cycle, such thatpower consumption can be optimized.

In addition, pixels to be activated in the pixel array 1005 may bechanged from pixels of the first direct pixel group 1020 to pixels ofthe second direct pixel group 1030 or may be changed from pixels of thesecond direct pixel group 1030 to pixels of the first direct pixel group1020, such that effects similar to those of a light beam of a radarsystem configured to rotate by 360° can be obtained.

Although the above-mentioned embodiment of the disclosed technology hasdisclosed that the first direct pixel group 1020 is first activated forconvenience of description, the scope or spirit of the disclosedtechnology is not limited thereto, and the second direct pixel group1030 according to another embodiment can be activated first asnecessary. In addition, although the above-mentioned embodiment of thedisclosed technology has disclosed that the entire direct cycle canextend to at least the twelfth direct cycle DC12 for convenience ofdescription, the scope or spirit of the disclosed technology is notlimited thereto. If the predetermined condition described in step S30shown in FIG. 3 is satisfied in any other steps prior to reaching thetwelfth direct cycle DC12, the operation mode of the image sensingdevice 1000 may switch from the object monitoring mode to the depthresolving mode.

If the operation mode of the image sensing device 1000 switches from theobject monitoring mode to the depth resolving mode, the indirect cycle(IC) may be started. In the indirect cycle (IC), the indirect pixels1040 and the constituent elements 1050, 1060, and 1090 for controllingand reading out the indirect pixels 1040 may be activated. In theindirect cycle (IC), the indirect pixels 1040 can be activated at thesame time. In addition, the direct pixels 1010 and the constituentelements 1070 and 1080 for controlling and reading out the direct pixels1010 may be deactivated.

FIG. 12 is a conceptual diagram illustrating another example ofoperations of the image sensing device 100 shown in FIG. 1 based on someimplementations of the disclosed technology.

The image sensing device 1200 shown in FIG. 12 may illustrate anotherexample of some constituent elements included in the image sensingdevice 100 shown in FIG. 1. The image sensing device 1200 may include apixel array 1205, a row driver 1250, a modulation driver 1260, ahorizontal TDC 1270, a vertical TDC 1280, and an indirect readoutcircuit 1290. The remaining components of the image sensing device 1200other than some structures different from those of the image sensingdevice 1000 may be substantially similar in structure and function tothose of the image sensing device 1000 shown in FIG. 10, and as suchredundant description thereof will herein be omitted for brevity. Forconvenience of description, the image sensing device 1200 shown in FIG.12 will hereinafter be described centering upon characteristicsdifferent from those of the image sensing device 1000 shown in FIG. 10.

The pixel array 1205 may further include a third direct pixel group 1225and a fourth direct pixel group 1235, each of which includes a pluralityof direct pixels 1210. The entire region and detailed operations of thedirect pixels 1210 included in each of the third and fourth direct pixelgroups 1225 and 1235 may be substantially identical to those of thedirect pixels 1210.

The third direct pixel group 1225 may include a plurality of directpixels 1210 arranged in a line in a horizontal direction (or a rowdirection) of the pixel array 1205.

The fourth direct pixel group 1235 may include a plurality of directpixels 1210 arranged in a line in a vertical direction (or a columndirection) of the pixel array 1205.

The first direct pixel group 1220 and the second direct pixel group 1230may be defined as a first set. The third direct pixel group 1225 and thefourth direct pixel group 1235 may be defined as a second set.

A central pixel disposed at a crossing point of the first to fourthdirect pixels groups 1220, 1225, 1230, and 1235 may be included in eachof the first to fourth direct pixel groups 1220, 1225, 1230, and 1235.

On the other hand, the horizontal TDC 1270 may be coupled to each directpixel 1210 included in the first direct pixel group 1220 and each directpixel 1210 included in the third direct pixel group 1225. Each directpixel 1210 of the first direct pixel group 1220 and each direct pixel1210 of the third direct pixel group 1225, that are arranged in a linein the column direction, may be coupled to the same signal line, and thehorizontal TDC 1270 may include a plurality of TDC circuits eachcorresponding to a set of two direct pixels 1210.

The vertical TDC 1280 may be coupled to each direct pixel 1210 includedin the second direct pixel group 1230 and each direct pixel 1210included in the fourth direct pixel group 1235. Each direct pixel 1210of the second direct pixel group 1230 and each direct pixel 1210 of thefourth direct pixel group 1235, that are arranged in a line in thecolumn direction, may be coupled to the same signal line, and thevertical TDC 1280 may include a plurality of TDC circuits eachcorresponding to a set of two direct pixels 1210.

FIG. 13 is a conceptual diagram illustrating an example of operations ofthe image sensing device shown in FIG. 12 based on some implementationsof the disclosed technology.

Referring to FIGS. 12 and 13, when the image sensing device 1200operates in each of the object monitoring mode and the depth resolvingmode, information about how pixels are activated according to lapse oftime are illustrated. In this case, activation of such pixels may referto an operation state in which each pixel receives a control signal fromthe corresponding pixel driver 120 or 130, generates a signal (e.g., apulse signal or a pixel signal) acquired by detection of incident light,and transmits the generated signal to the corresponding readout circuit140 or 150. In FIG. 13, the activated pixels may be represented byshaded pixels.

In the object monitoring mode in which the image sensing device 1200generates digital data indicating the distance to the target objectusing the direct TOF method, the image sensing device 1200 may operatesequentially in units of a direct cycle (or on a direct-cycle basis). Ascan be seen from FIG. 13, the image sensing device 1200 may sequentiallyoperate in the order of first to twelfth direct cycles DC1˜DC12. Each ofthe first to twelfth direct cycles DC1˜DC12 may refer to a time periodin which a series of operations including, for example, an operation ofemitting pulse light to the target object 1, an operation of generatinga pulse signal corresponding to reflected light received from the targetobject 1, an operation of generating digital data corresponding to thepulse signal, the quenching operation, and the recharging operation, canbe performed. For example, the time period t1˜t2 or t2˜t3 shown in FIG.9 may correspond to a single direct cycle.

In the first direct cycle DC1, the direct pixels 1210 included in eachof the first direct pixel group 1220 and the second direct pixel group1230 that correspond to the first set may be activated, and the directpixels 1210 included in each of the third direct pixel group 1225 andthe fourth direct pixel group 1235 that correspond to the second set maybe deactivated. The horizontal TDC 1270 for processing the pulse signalof the first direct pixel group 1220 and the vertical TDC 1280 forprocessing the pulse signal of the second direct pixel group 1230 may beactivated. In addition, the indirect pixels 1240, and the constituentelements 1250, 1260, and 1290 for controlling and reading out theindirect pixels 1240 may be deactivated.

In the second direct cycle DC2, the direct pixels 1210 included in eachof the first direct pixel group 1220 and the second direct pixel group1230 that correspond to the first set may be deactivated, and the directpixels 1210 included in each of the third direct pixel group 1225 andthe fourth direct pixel group 1235 that correspond to the second set maybe activated. The horizontal TDC 1270 for processing the pulse signal ofthe third direct pixel group 1225 and the vertical TDC 1280 forprocessing the pulse signal of the fourth direct pixel group 1235 may beactivated at the same time. In addition, the indirect pixels 1240, andthe constituent elements 1250, 1260, and 1290 for controlling andreading out the indirect pixels 1240 may be deactivated.

Not only in the third to twelfth direct cycles DC3˜DC12, but also insubsequent direct cycles, the direct pixels 1210 included in the firstand second direct pixel groups 1220 and 1230 and the direct pixelsincluded in the third and fourth direct pixel groups 1225 and 1235 maybe alternately activated in the same manner as in the first direct cycleDC1 and the second direct cycle DC2.

Therefore, a minimum number of the direct pixels having relativelylarger power consumption may be included in the pixel array 1205, andonly some of the direct pixels may be activated within one direct cycle,such that the amount of power consumption can be optimized.

In addition, pixels to be activated in the pixel array 1205 may bechanged from the direct pixels 1210 (i.e., the first and second directpixel groups 1220 and 1230) arranged in the diagonal direction to thedirect pixels 1210 (i.e., the third and fourth direct pixel groups 1225and 1235) arranged in the horizontal and vertical directions, or may bechanged from the direct pixels 1210 arranged in the horizontal andvertical directions to the direct pixels 1210 arranged in the diagonaldirection, such that effects similar to those of a light beam of a radarsystem can be obtained.

Although the above-mentioned embodiment of the disclosed technology hasdisclosed that the first and second direct pixel groups 1220 and 1230are first activated for convenience of description, the scope or spiritof the disclosed technology is not limited thereto, and the third andfourth direct pixel groups 1225 and 1235 according to another embodimentcan be activated first as necessary. Although FIG. 13 has disclosed thattwo direct pixel groups are simultaneously activated in each directcycle, it should be noted that only one direct pixel group may beactivated in each direct cycle based on some other implementations ofthe disclosed technology. For example, the first direct pixel group1220, the fourth direct pixel group 1235, the second direct pixel group1230, and the third direct pixel group 1225 may be sequentiallyactivated clockwise, such that effects similar to those of a light beamof a radar system can be obtained.

In addition, although the above-mentioned embodiment of the disclosedtechnology has disclosed that the entire direct cycle can extend to atleast the twelfth direct cycle DC12 for convenience of description, thescope or spirit of the disclosed technology is not limited thereto, andother implementations are also possible. For example, if thepredetermined condition described in step S30 shown in FIG. 3 issatisfied in any other steps prior to reaching the twelfth direct cycleDC12, the operation mode of the image sensing device 1200 may switchfrom the object monitoring mode to the depth resolving mode.

If the operation mode of the images sensing device 1200 switches fromthe object monitoring mode to the depth resolving mode, the indirectcycle (IC) may be started. In the indirect cycle (IC), the indirectpixels 1240 and the constituent elements 1250, 1260, and 1290 forcontrolling and reading out the indirect pixels 1240 may be activated.In addition, the direct pixels 1210 and the constituent elements 1270and 1280 for controlling and reading out the direct pixels 1210 may bedeactivated.

As is apparent from the above description, the image sensing devicebased on some implementations of the disclosed technology can beequipped with different sensing pixels and associated circuitry forperforming TOF measurements based on different TOF measurementtechniques with different TOF sensing capabilities so that the devicecan select an optimum TOF method in response to a distance to a targetobject, such that the image sensing device can sense the distance to thetarget object using the optimum TOF method.

The embodiments of the disclosed technology may be implemented invarious ways to achieve one or more advantages or desired effects.

Although a number of illustrative embodiments have been described, itshould be understood that numerous modifications or enhancements to thedisclosed embodiments and other embodiments can be devised based on whatis described and/or illustrated in this patent document.

What is claimed is:
 1. An image sensing device comprising: a pixel arrayconfigured to include at least one first pixel and at least one secondpixel; and a timing controller configured to activate either the firstpixel or the second pixel based on a distance between a target objectand the pixel array, wherein the first pixel and the second pixel havedifferent characteristics that include at least one of an effectivemeasurement distance related to an ability to effectively sense adistance, a temporal resolution related to an ability to discern atemporal difference, a spatial resolution related to an ability todiscern a spatial difference, or unit power consumption indicating anamount of power required to generate a pixel signal.
 2. The imagesensing device according to claim 1, wherein the first pixel correspondsto a single-photon avalanche diode (SPAD) pixel.
 3. The image sensingdevice according to claim 1, wherein the first pixel includes: asingle-photon avalanche diode (SPAD) configured to generate a currentpulse by sensing a single photon reflected from the target object; aquenching circuit configured to control a reverse bias voltage appliedto the single-photon avalanche diode (SPAD); and a digital bufferconfigured to convert the current pulse into a digital pulse signal. 4.The image sensing device according to claim 1, wherein: the first pixelcorresponds to a direct pixel configured to sense the distance to thetarget object using time for light reflected from the target object; andthe second pixel corresponds to an indirect pixel configured to sensethe distance to the target object using a phase of light reflected fromthe target object.
 5. The image sensing device according to claim 1,wherein: the first pixel is included in: a first direct pixel group inwhich the plurality of first pixels is arranged in a line in a firstdiagonal direction; or a second direct pixel group in which theplurality of first pixels is arranged in a line in a second diagonaldirection.
 6. The image sensing device according to claim 5, furthercomprising: a horizontal time-to-digital circuit (TDC) disposed at oneside of the pixel array, and configured to process an output signal ofthe first direct pixel group; and a vertical time-to-digital circuit(TDC) disposed at the other side of the pixel array, and configured toprocess an output signal of the second direct pixel group.
 7. The imagesensing device according to claim 5, wherein: in a first direct cycle inwhich the first pixel is activated, any one of the first direct pixelgroup and the second direct pixel group is activated; and in a seconddirect cycle subsequent to the first direct cycle, the other one of thefirst direct pixel group and the second direct pixel group is activated.8. The image sensing device according to claim 1, wherein: the firstpixel is included in any one of: a first direct pixel group in which theplurality of first pixels is arranged in a line in a first diagonaldirection; a second direct pixel group in which the plurality of firstpixels is arranged in a line in a second diagonal direction; a thirddirect pixel group in which the plurality of first pixels is arranged ina line in a horizontal direction; and a fourth direct pixel group inwhich the plurality of first pixels is arranged in a line in a verticaldirection.
 9. The image sensing device according to claim 8, furthercomprising: a horizontal time-to-digital circuit (TDC) disposed at oneside of the pixel array, and configured to process an output signal ofthe first direct pixel group and an output signal of the third directpixel group; and a vertical time-to-digital circuit (TDC) disposed atthe other side of the pixel array, and configured to process an outputsignal of the second direct pixel group and an output signal of thefourth direct pixel group.
 10. The image sensing device according toclaim 8, wherein: in a first direct cycle in which the first pixel isactivated, any one of a first set including the first direct pixel groupand the second direct pixel group and a second set including the thirddirect pixel group and the fourth direct pixel group is activated; andin a second direct cycle subsequent to the first direct cycle, the otherone of the first set and the second set is activated.
 11. The imagesensing device according to claim 1, wherein the second pixel includes:a photoelectric conversion element configured to generate and accumulatephotocharges by performing photoelectric conversion of incident lightreflected from the target object; a plurality of circulation gatesdisposed in regions corresponding to four sides of a rectangular ringshape surrounding the photoelectric conversion element, and configuredto induce movement of the photocharges by partially generating anelectric field in different regions of the photoelectric conversionelement based on circulation control voltages; and a plurality oftransfer gates disposed in regions corresponding to vertex points of therectangular ring shape, and configured to transmit the photocharges to acorresponding floating diffusion (FD) region based on transfer controlsignals.
 12. The image sensing device according to claim 1, wherein thepixel array includes one or more additional first pixels and one or moreadditional second pixels and a total size of a region for the firstpixel and the one or more additional first pixels is smaller than atotal size of a region for the second pixel and the one or moreadditional second pixels.
 13. The image sensing device according toclaim 1, wherein: the first pixel is larger in size than the secondpixel.
 14. The image sensing device according to claim 1, wherein: thepixel array includes one or more additional first pixels and one or moreadditional second pixels and the second pixel and the one or moreadditional second pixels are arranged in a matrix shape.
 15. The imagesensing device according to claim 14, wherein the second pixel and theone or more additional second pixels are activated at a same time.
 16. Aphotographing device comprising: an image sensing device configured tohave a first pixel and a second pixel different from the first pixel inhaving different values of at least one of an effective measurementdistance related to an ability to effectively sense a distance, temporalresolution related to an ability to discern a temporal difference,spatial resolution related to an ability to discern a spatialdifference, or unit power consumption indicating an amount of powerrequired to generate a pixel signal; and an image signal processorconfigured to operate the image sensing device in an object monitoringmode in which the first pixel is activated or a depth resolving mode inwhich the second pixel is activated based on a comparison between apredetermined threshold distance and a distance between the imagesensing device and a target object.
 17. The photographing deviceaccording to claim 16, wherein the image signal processor is furtherconfigured to increase a counted resultant value by a predeterminedvalue based on the comparison; and switch an operation mode of the imagesensing device from the object monitoring mode to the depth resolvingmode based on the increased counted resultant value.
 18. Thephotographing device according to claim 16, wherein the first pixel isconfigured to measure a distance to the target object using time forlight reflected from the target object and the second pixel isconfigured to measure the distance to the target object using a phase oflight reflected from the target object.
 19. A sensing device capable ofdetecting a distance to an object comprising: one or more first sensingpixels configured to detect light and measure a distance to a targetobject based on a first distance measuring technique; a first pixeldriver coupled to and operable to control the one or more first sensingpixels in detecting light for measuring the distance; one or more secondsensing pixels configured to detect light and measure a distance to atarget object based on a second distance measuring technique that isdifferent from the first distance measuring technique so that the firstand second distance measuring techniques have different distancemeasuring characteristics; a second pixel driver coupled to and operableto control the one or more second sensing pixels in detecting light formeasuring the distance; and a controller configured to activate eitherthe one or more first sensing pixels or the one or more second sensingpixels based on the different distance measuring characteristics of thefirst and second sensing pixels with respect to a distance between thetarget object and the sensing device.
 20. The sensing device as in claim19, wherein the different distance measuring characteristics of thefirst and second sensing pixels include, a range of distance that can bemeasured, a spatial resolution in distance measurements, a time neededfor a sensing pixel in performing a distance measurement, or powerconsumed by a sensing pixel in performing a distance measurement.